What is systematic theology?

An open Bible laying flat on a table

This article represents my collection of notes and personal thoughts on the “Basics of Systematic Theology: Scripture” lecture by Scott R. Swain, Ph.D. at Reformed Theological Seminary in 2017. All unattributed quotations are those of Dr. Swain.

Scott Swain lecturing on systematic theology

What is systematic theology?

On the surface, systematic theology may seem very dry, as if the stories and messages found within the Bible are pulled out and systematized into stale Latin phrases by dead theologians. But systematic theology is much richer. It’s a way of studying a subject in context throughout the entirety of Scripture, attending to the cohesiveness of texts separated by thousands of years, dozens of authors, and multiple languages and cultures. In his lecture introducing systematic theology, Scott R. Swain highlights four key principles: unity, scope, proportion, and relationships.


How do the books of the Bible relate to one another to form a unified message? In systematic theology, we ask not just, ‘What does Paul say in Romans,’ but, ‘how does what Paul says in Romans relate to what Moses says in Exodus?’ Furthermore, the principle of unity in systematic theology also attempts to relate the teachings of the Bible with science and philosophy.

Full scope

Systematic theology attempts to read and interpret Scripture in light of the rest of Scripture. In Acts 20, while addressing the elders of the church in Ephesus, Paul declares that he did not shrink from declaring to you the whole counsel of God. (v. 27, ESV)

The Dutch Reformed theologian Herman Bavinck (1854–1921) noted that failure to observe the full scope of Scripture leads to one-sidedness and error in theology and pathology in the religious life.


Scott Swain illustrates the point that systematic theology observes biblical proportions in this way: The Bible says something about everything… But the Bible doesn’t say everything about everything. There are first-order matters and second-order matters in Scripture.1 As Paul points out in 1 Corinthians 152, the gospel is a matter of first importance. And though the Bible frequently mentions animals of various kinds, biblical information about animals is a matter of much lower importance than what the Bible says about human salvation. Systematic theology attempts to define those distinctions.


The fourth principle of systematic theology is concerned with the relationships between various doctrines. Swain uses the examples of good works and grace. Both of these doctrines are important to the Christian life. But how do good works and grace interact with each other? If we think that good works are the basis for God’s grace, we’re going to get ourselves in all kinds of trouble. That’s because good works come after grace, not before. Systematic theology studies the relationships between doctrines in order to clarify each doctrine.

8 For it is by grace you have been saved, through faith—and this is not from yourselves, it is the gift of God— 9 not by works, so that no one can boast. 10 For we are God’s handiwork, created in Christ Jesus to do good works, which God prepared in advance for us to do.

Ephesians 2:8–10, NIV


What can the study of systematic theology tell us about Scripture? Is the Bible reliable and authoritative? Is it inspired by God or just a collection of writings by mortal men? Since all theological study necessarily deals primarily with holy texts, the study of Scripture itself is a good place to start. Swain employs three passages in order to observe how the Bible’s authors viewed Scripture.

God is pleased to reveal himself to us in order that we might find rest in him.

25 At that time Jesus said, I praise you, Father, Lord of heaven and earth, because you have hidden these things from the wise and learned, and revealed them to little children. 26 Yes, Father, for this is what you were pleased to do. 27 All things have been committed to me by my Father. No one knows the Son except the Father, and no one knows the Father except the Son and those to whom the Son chooses to reveal him. 28 Come to me, all you who are weary and burdened, and I will give you rest. 29 Take my yoke upon you and learn from me, for I am gentle and humble in heart, and you will find rest for your souls. 30 For my yoke is easy and my burden is light.

Matthew 11:25–30, NIV

In Matthew 11, we discover that the Godhead—Father, Son, Holy Spirit—are complete in their unity of knowledge and love with one another. This passage also teaches us that the Father delights in making himself known to his children. This knowledge of God that is revealed to us is not only for God’s good pleasure, but also so that we may find rest in him.

You have made us for yourself, O Lord, and our hearts are restless until they rest in You.
— Augustine, Confessions

God is pleased to reveal himself to us in a twofold manner.

1 For the director of music. A psalm of David.

The heavens declare the glory of God;
the skies proclaim the work of his hands.
2 Day after day they pour forth speech;
night after night they reveal knowledge.
3 They have no speech, they use no words;
no sound is heard from them.
4 Yet their voice goes out into all the earth,
their words to the ends of the world.
In the heavens God has pitched a tent for the sun.
5 It is like a bridegroom coming out of his chamber,
like a champion rejoicing to run his course.
6 It rises at one end of the heavens
and makes its circuit to the other;
nothing is deprived of its warmth.

7 The law of the Lord is perfect,
refreshing the soul.
The statutes of the Lord are trustworthy,
making wise the simple.
8 The precepts of the Lord are right,
giving joy to the heart.
The commands of the Lord are radiant,
giving light to the eyes.
9 The fear of the Lord is pure,
enduring forever.
The decrees of the Lord are firm,
and all of them are righteous.

10 They are more precious than gold,
than much pure gold;
they are sweeter than honey,
than honey from the honeycomb.
11 By them your servant is warned;
in keeping them there is great reward.
12 But who can discern their own errors?
Forgive my hidden faults.
13 Keep your servant also from willful sins;
may they not rule over me.
Then I will be blameless,
innocent of great transgression.

14 May these words of my mouth and this meditation of my heart
be pleasing in your sight,
Lord, my Rock and my Redeemer.

Psalm 19, NIV

In Psalm 19, we can decipher two “books” by which we can know God: the book of nature and the book of Scripture. The Belgic Confession reads:

We know Him by two means: First, by the creation, preservation, and government of the universe; which is before our eyes as a most elegant book, wherein all creatures, great and small, are as so many characters leading us to see clearly the invisible things of God, even his everlasting power and divinity, as the apostle Paul says (Romans 1:20). All which things are sufficient to convince men and leave them without excuse. Second, He makes Himself more clearly and fully known to us by His holy and divine Word, that is to say, as far as is necessary for us to know in this life, to His glory and our salvation.

Belgic Confession, Article 2

The theological term “general revelation” is typically used of the work of the book of nature, while theologians use “special revelation” to describe knowledge that comes from the inspired Word of God, the book of Scripture.

In verses 1–6 of Psalm 19, the natural world is said to declare the glory of God (v. 1) and the psalmist makes use of metaphorical language to describe the eagerness of the sun to warm the whole earth. That’s general revelation, which describes human observance of the splendor of nature. General revelation is available to all audiences, but it is incomplete and cannot, by itself, bring us into a relationship with God. That’s where special revelation comes in. The psalmist references human anatomy in verses 7 and 8 to illustrate the incompleteness of the parts on their own until they are brought together by the work of God’s law, statutes, and precepts. The soul, mind (v. 7), heart, and eyes (v. 8), themselves works of nature, are given refreshment, wisdom, joy, and light when introduced to the special revelation of God.

Not only does Psalm 19 show us how these two books speak to us about God, but the psalmist also teaches us how we should speak back to God. In verses 12 and 13, he says, But who can discern their own errors? Forgive my hidden faults. Keep your servant also from willful sins; may they not rule over me. The psalmist, King David, acknowledges that he is out of step with the rest of nature in glorifying God—both unintentionally and willfully sinning against the Lord. Finally, in verse 14, he says, May these words of my mouth and this meditation of my heart be pleasing in your sight, Lord, my Rock and my Redeemer. David knows that he cannot earn God’s favor, but he appeals to God’s graciousness in his relationship with his creator. Though I am a sinner, may the words I speak and the reflections of my heart demonstrate a deep love for God.

“Until Jesus returns, the Bible is our supreme source of special revelation”

16 For we did not follow cleverly devised stories when we told you about the coming of our Lord Jesus Christ in power, but we were eyewitnesses of his majesty. 17 He received honor and glory from God the Father when the voice came to him from the Majestic Glory, saying, This is my Son, whom I love; with him I am well pleased. 18 We ourselves heard this voice that came from heaven when we were with him on the sacred mountain. 19 We also have the prophetic message as something completely reliable, and you will do well to pay attention to it, as to a light shining in a dark place, until the day dawns and the morning star rises in your hearts. 20 Above all, you must understand that no prophecy of Scripture came about by the prophet’s own interpretation of things. 21 For prophecy never had its origin in the human will, but prophets, though human, spoke from God as they were carried along by the Holy Spirit.

2 Peter 1:16–21, NIV

The Bible is God’s inspired word, and Dr. Swain points to this passage from the apostle Peter’s second letter as the best declaration in Scripture of the Bible’s own inspiration. He notes two things that this passage teaches us. (There are actually more than two.)

The first thing that this passage teaches is that prophets and apostles had special access to God’s revelations. They did not simply interpret events happening around them as being related in some way to God, filling in the gaps of their observations with contrivances. Secondly, each prophet and apostle had a special anointing from the Holy Spirit, allowing them to remember what they saw and reliably communicate it to us.

This passage also affirms the unity of Scripture. What the prophets foretold, the apostles witnessed. As Swain notes toward the end of his lecture, All of Scripture holds together as a testimony to Christ.

The Bible is inspired. It’s unified. And it’s sufficient. Earlier in the chapter, Peter writes, His divine power has given us everything we need for a godly life through our knowledge of him who called us by his own glory and goodness (v. 3, emphasis added). In addition, Scripture is reliable and authoritative (v. 19). It’s also clear. The Bible is not always clear, as Peter himself acknowledges later in this letter3, but the basic message of Scripture is clear: God desires for humanity to know him and share in his rest, and his love for us is so great that he redeemed us for union with himself forever.

Scott Swain’s final point looks to the second half of verse 19: …as to a light shining in a dark place, until the day dawns and the morning star rises in your hearts. Scripture is our supreme source of special revelation right now—until the second advent of Christ. As we await with eagerness the blessed hope—the appearing of the glory of our great God and Savior, Jesus Christ (Titus 2:13, NIV), we have at present a lamp for [our] feet, a light on [our] path (Psalm 119:105, NIV).

The Bible is inspired, unified, sufficient, reliable, authoritative, and clear. Scripture is from God, about God, and leads us to God, where we will find rest for [our] souls (Matthew 11:29). Amen.

  1. There are certainly matters of even lower importance. 

  2. For I delivered to you as of first importance what I also received: that Christ died for our sins in accordance with the Scriptures, that he was buried, that he was raised on the third day in accordance with the Scriptures, and that he appeared to Cephas, then to the twelve. (1 Corinthians 15:3–5, ESV) 

  3. Speaking of Paul, Peter writes, His letters contain some things that are hard to understand. (2 Peter 3:16, NIV)