Summa Theologica

How can you truly know God, not merely through belief but through reason itself? In Catechism of the Summa Theologica, Dominican theologian R. P. Thomas Pègues masterfully condenses St. Thomas Aquinas’ monumental Summa Theologica into a clear, question-and-answer guide for the faithful. His aim is audacious yet simple: to make the Church’s most profound theology accessible to ordinary men and women. Drawing upon centuries of scholastic insight, Pègues argues that divine truth can be understood through structured reasoning just as much as through revelation. Faith, he insists, is not blind—it is illuminated by reason, ordered by virtue, and perfected through grace.

This book explores nearly every dimension of Christian thought: the existence and nature of God; creation and the hierarchy of angels and men; the role of free will and sin; the purpose of law and grace; and ultimately, the journey of the soul to union with God. Aquinas’ timeless framework—God as the First Cause, man as the rational creature who must return to his Creator—serves as the foundation of Western theological philosophy. Pègues renders this immense system readable, conversational, and deeply personal, turning what might seem abstract into an invitation to live according to wisdom itself.

From Complexity to Clarity

The original Summa Theologica is vast—over three thousand pages structured as arguments, objections, and responses. Pègues simplifies it into catechetical form: direct questions such as “Does God exist?” or “Can angels move from place to place?” answered succinctly and logically. This format transforms the intimidating scholastic method into an ongoing conversation with reason. Through this structure, readers engage actively, testing belief against understanding. In essence, you don’t merely read theology—you practice it.

Faith Meets Reason

For Aquinas and for Pègues alike, faith and reason are not enemies but companions. The book argues that rational thought confirms divine revelation. You can know that God exists because all things that do not exist on their own must depend on something that does—a chain of causation that ends in God, the First Cause. This logical proof is not an alternative to faith but its foundation. You believe because your reason perceives order and truth in the world; faith deepens that recognition by accepting what reason cannot itself reach—the mysteries of the Trinity, the Incarnation, and grace.

The Divine Order: God, Angels, Humanity

The Catechism follows Aquinas’ three-part structure: God, Man, and Christ. First, it unveils the nature of God—the infinite, eternal, unchangeable, omnipresent being who is pure act, pure being, and pure good. Second, it describes creation not as necessity but as love overflowing: angels, humans, and the cosmos as reflections of divine order. Finally, it presents Christ as the bridge restoring man’s fallen nature to God’s eternal purpose. Each stage of this hierarchy flows from God's perfection and aims at man's sanctification.

Why It Matters Today

In a modern world often skeptical of metaphysical truth, Pègues’ adaptation reminds you that theology offers more than doctrine—it offers meaning. To understand creation as purposeful and moral law as participation in divine wisdom transforms every action into worship. Whether you seek intellectual clarity or spiritual depth, this catechism invites you to see the universe as Aquinas saw it: not a random collection of beings, but a luminous order, sustained by God and destined to return to Him. In reading, you encounter not only a philosophical system but the heartbeat of Christian faith—the soul’s journey toward the infinite Good.

Pègues begins where philosophy itself begins—with the question, Does God exist? His reaffirmation of Aquinas’ classical proofs for God’s existence forms the cornerstone of the catechism’s intellectual architecture. You are led through logical analysis rather than mere assertion: if something exists but not by its own power, it must depend on something that does. Ultimately, this chain of dependency ends with a being that exists of itself—God, the necessary being upon which all else depends.

Contingent Beings and the First Cause

Every object around you is contingent—it could fail to exist, and it depends on many causes. Your body depends on parents, your parents on the human species, and so on. Aquinas’ reasoning (and echoed by Pègues) insists that this progression cannot go backward infinitely; there must be a first, uncaused cause—God Himself. The very existence of dependence proves independence somewhere higher up the chain. Without this ultimate ground of being, nothing could exist at all.

The Fool Who Denies God

For Aquinas, disbelief is not simply an intellectual error; it’s an irrational contradiction. As Psalm 14 declares—“The fool says in his heart, there is no God.” Pègues elaborates: denying the existence of God means asserting that what needs everything to exist needs nothing at all—an absurdity. In essence, atheism collapses under its own logic. Every dependency in nature cries out for its ultimate foundation; to deny it is to embrace incoherence.

Reason and Revelation in Harmony

Aquinas’ proof does not weaken faith—it purifies it. Pègues writes that faith becomes more luminous when reason approaches its source. Just as sunlight makes colors visible, so logical inquiry makes revelation intelligible. In contrast to existentialist doubt or modern skepticism (e.g., Nietzsche’s and Sartre’s rejection of metaphysical necessity), Aquinas places intellect in service to wonder: reason’s highest act is not autonomy but adoration.

Once God’s existence is proved, Aquinas—and Pègues after him—reveals who God is. God is pure spirit, without body or composition, infinitely perfect, unchangeable, eternal, and one. He is not merely a being among beings but Being Itself. This idea transforms your understanding: God isn't an object that exists within the universe; He is the reason the universe can exist at all.

Perfection and Goodness

God lacks nothing—He is the fullness of perfection. His goodness is intrinsic, not borrowed, and in Him love begins and ends. To call God good, Aquinas notes, isn’t analogy but identity: whatever we mean by goodness finds its source in Him. This insight changes how you pray and think—you seek goodness not outside but within the divine essence.

Infinity, Omnipresence, and Eternity

God’s infinity means no boundaries limit His being. He is everywhere—not as one point among many, but because all things exist in Him and through Him. Eternity, equally, is not endless time but absence of succession. In God there is no “before” or “after”—He comprehends all in a single, unchanging act. You live in time; God lives in pure actuality.

Knowing God: Reason and Faith

You cannot see God with mortal eyes; your body blocks such vision. Yet your reason perceives Him dimly through His creation, and faith—His self-revelation—makes this vision luminous. Pègues insists that knowledge by faith surpasses knowledge by intellect: in faith you glimpse the dawn of beatitude, the light by which heaven’s glory will someday illumine your soul. The mind reasons toward God; the heart believes into Him.

How does God act within creation once He has made it? Aquinas calls this divine activity Providence—God’s continuous care governing all things toward their end. Pègues unfolds this concept with clarity: God’s will directs every creature, from angel to atom, with wisdom that harmonizes freedom and necessity. Nothing escapes His sight; every motion serves the divine purpose whether through direct causing or permitted freedom.

The Justice and Mercy of Divine Rule

God’s providence is not cold determinism but personal love in order. He rewards the good and punishes the wicked, both in this life and the next. Yet His justice never excludes mercy—He gives more than is due to goodness and punishes less than evil deserves. Pègues assures readers that this duality of justice and mercy defines the divine character: punishment corrects; mercy perfects.

Predestination and Human Freedom

Predestination—a term often misunderstood—is here revealed as the ultimate expression of divine love. Those whom God chooses for heaven He predestines by grace, arranging all their circumstances toward salvation. Yet man’s freedom remains intact: you are free to respond or reject. Refusal does not defy His sovereignty but fulfills justice. Aquinas’ harmony of grace and freedom contrasts sharply with later deterministic theology (as seen in Calvinism), emphasizing instead divine wisdom that respects liberty while ensuring cosmic order.

The Call to Trust Providence

Thinking of God’s eternal plan inspires humility. Pègues exhorts you not to fear chaos—creation is governed by meaning. Even suffering and apparent evil participate in a larger design where universal good shines forth. To trust Providence is to see miracles in ordinary life: a harmony concealed today that eternity will one day reveal completely.

Aquinas’ cosmology, summarized by Pègues, presents creation as a harmonious hierarchy reflecting divine wisdom. The world comprises pure spirits (angels), bodies, and beings combining both (men). Each fulfills a distinct role in manifesting God’s glory. Angels are the crown of creation’s spiritual order, while man, uniting spirit and body, harmonizes matter and intellect—bridging heaven and earth.

The Angelic Orders

Angels, according to Pègues’ catechism, are innumerable pure spirits divided into nine choirs: Seraphim, Cherubim, Thrones, Dominations, Virtues, Powers, Principalities, Archangels, and Angels. Each hierarchy reflects a different way of knowing and serving God—some directly adore Him, others govern creation’s laws, and others guard humankind. You, as a person, live every day under the watchful protection of one of these celestial beings, your guardian angel assigned by divine ordinance.

Man’s Place in Creation

Man, however, holds unique dignity as the only creature made in both matter and spirit. The human soul is immortal, rational, and free. Through intellect, man touches the divine; through body, he interacts with the material universe. Because his reason is imperfect, he relies on faith and grace to ascend toward his Creator. In this way, humanity completes the cosmic order—the link between heaven’s purity and earth’s substance.

The Order of Love

This hierarchy is not tyranny but love’s harmony. Angels enlighten one another as rivers flowing from God’s mountain; they impart divine wisdom in cascades of understanding. Humanity participates in this cosmic symphony through its vocation: to know, to love, and to return to God. In your own intellect and will—your capacity to understand and choose—you mirror the angelic life on earth. Every act of truth and love joins this hierarchy in praising the Creator.

At the center of the Catechism lies Aquinas’ profound moral philosophy: how should man, endowed with free will, act in harmony with divine reason? Pègues identifies this harmony in the natural and divine law—the moral structure of the universe. You, as a rational creature, participate in God’s eternal law through reason and conscience. To live rightly is to align your will with divine truth.

The Four Kinds of Law

Aquinas divides law into four kinds: eternal law (God’s wisdom governing all); natural law (human reason’s participation in this wisdom); human law (civil regulations derived from natural law); and divine law (revealed commands like the Decalogue). This structure balances freedom with order. The very sense of right and wrong within you mirrors divine wisdom.

Virtue and Sin

Virtue for Aquinas is a habit that makes both intention and action good; sin is its opposite. Mortal sins—those destroying charity—kill the soul, while venial ones merely wound it. Law instructs, but grace heals. In cultivating virtues—prudence, justice, fortitude, and temperance—you shape your freedom toward the good. As Pègues reminds, liberty isn’t doing what you want; it’s wanting what reason and grace reveal as right.

Law, Grace, and Divine Friendship

Grace does not abolish law—it animates it. By grace you are elevated from being merely citizen under law to child under love. Pègues speaks of divine friendship: grace makes your actions meritorious before God not as servile obedience but as filial cooperation. Thus, moral life is not restriction but invitation—a participation in the divine reason that created the universe.

In Aquinas’ grand scheme, man’s return to God unfolds through three theological virtues: faith, hope, and charity. Pègues explains these with pastoral warmth, turning metaphysical principles into living practice. Faith directs the mind toward divine truth; hope lifts the will toward eternal joy; charity unites both in love. These virtues transcend all others because their object is God Himself.

Faith: Light of Understanding

Faith allows you to assent to truths beyond reason—accepting divine revelation because God, who is Truth Itself, cannot deceive. Pègues emphasizes that real faith involves interior humility: not blind belief, but confident trust in God’s word. Through faith, Aquinas says, the believer begins to see as heaven sees.

Hope: Trust in God’s Promises

Hope lifts the soul above despair and presumption. You trust that God’s mercy and power will lead you to Him. This virtue aligns with the gift of fear—not servile terror but filial reverence — preserving your relationship with God through awe and confidence. Hope transforms suffering into pilgrimage.

Charity: The Bond of Divine Love

Charity completes the circle. It is not mere affection but participation in God’s own love. Through charity you desire God for Himself and others for His sake. It births virtues like joy, peace, mercy, and kindness. In Pègues’ tender catechism, charity is described as the soul’s heartbeat—when it stops, all other life ceases. To live charitably is not optional; it is to live in God Himself.

The final section of Pègues' catechism brings theology from contemplation to participation: how grace comes to you concretely through the sacraments. Aquinas defines grace as divine help transforming human nature into childlike participation in the divine life. These sacraments—baptism, confirmation, Eucharist, penance, and others—are visible signs of invisible reality. They make holiness tangible, the way sunlight makes warmth felt.

Grace as Transformation

Habitual or sanctifying grace divinizes your soul, making you capable of living in friendship with God. Actual grace acts moment by moment, prompting good decisions and repentance. The Catechism continually insists you cannot save yourself but can cooperate with grace—you offer cooperation, God provides power. Grace elevates natural virtue into divine participation.

The Role of the Sacraments

Each sacrament channels specific grace: baptism gives spiritual birth; confirmation strengthens courage; Eucharist nourishes divine life; and penance restores the fallen soul. These physical actions—water, oil, bread—are not symbols only; they do what they represent. Pègues calls them God’s chosen instruments to heal human weakness.

Toward Eternal Union

Ultimately, grace and sacrament lead to glory—the vision of God and the resurrection of the body. For Aquinas, salvation is not escape but perfection: man’s intellect filled with truth, his will aflame with love, his body radiant with immortality. Pègues’ catechism ends in prayer to Christ: a call to live now what eternity will complete—adoration, wisdom, and love without end.