How does systematic theology work?

from the old testament

• Bibliography is the study of the nature of the Bible, showing that it is unlike any other ancient book. Scripture testifies to being words of God (Exodus 34:27; 2 Samuel 23:2), without error (Psalm 12:6), sufficient to navigate life (Psalm 119:105; Deuteronomy 8:3), unchanging (Isaiah 40:8), and defines His people (Exodus 24:7).
• Theology Proper (also known as Paterology) is the study of the Father. While the New Testament more clearly distinguishes the Father from the other two Persons of the Godhead, references in the Old Testament to “God” are generally references to the Father. We learn that God is the eternal, self-existent Creator (Genesis 1:1; Exodus 3:14), unique and holy (Exodus 15:11), rules sovereignty over everything and one (Psalm 103:19), and is unchanging and faithful (Malachi 3:6).
• Christology studies the Person and activities of Jesus Christ. While Jesus is not revealed until the New Testament, from the Old Testament we learn that a righteous seed will defeat evil (Genesis 3:15) and bring blessings to the nations (Genesis 12:3). Known as the Messiah, He would be born of a virgin and called Immanuel (“God with us”; Isaiah 7:14), arise from David’s royal line, suffer for the sins of many (Isaiah 53:4-6), and bring salvation (Isaiah 49:6).
• Pneumatology is the study of the Person and activities of the Holy Spirit. Scripture teaches that the Spirit was active in creation (Genesis 1:2), given to specific individuals to temporarily empower them for specific duties (Exodus 31:1-3; Judges 14:6), and would be more broadly poured out on God’s people in the future (Joel 2:28).
• Soteriology is the study of salvation. According to the Bible, salvation starts with the LORD (Psalm 3:8; Isaiah 43:11), is grounded in faith in God’s promises (Genesis 15:6), and was not by obeying laws but required a heart change (Deuteronomy 10:16; Ezekiel 36:26).
• Hamartiology is the study of sin and its impact on creation and humanity. Sin entered through Adam and Eve’s disobedience (Genesis 2:16b-17; Genesis 3:6, 19), is both individual and corporate (Exodus 32:7-8; Isaiah 1:4-6), and every man and woman is born with a sinful nature (Psalm 51:5). Apart from God intervening, our sin leads towards alienation of judgement (Isaiah 59:2; Ezekiel 18:20).
• Anthropology is the study of humanity, including creation, purpose, values, and meaning. The Bible teaches that we were created in God’s image (Genesis 1:27), to multiply and fill the earth (Genesis 1:28a), to rule over creation (Genesis 1:28b), to live to glorify God (Isaiah 43:6-7), and to live forever (Ecclesiastes 3:11).
• Angelology is the study of angels (including demons and Satan). Scripture reveals a little about their creation (Job 38:4-7) and the fall of some (Isaiah 14:12-15; Ezekiel 28:12-17). The Bible shows that hey carry out God’s will (Psalm 103:20), deliver messages (Genesis 19:1ff), and have different roles (Isaiah 6:3; Psalm 91:11; Daniel 10:12-13).
• Eschatology is the study of last things or the end times, especially focused on yet unfulfilled biblical prophecies. God’s word says there will be a “day of the LORD” where God will judge Israel and the nations (Joel 2:1-11; Isaiah 13:6-13). Scripture promises restoration and renewal, through the creation of new hearts (Jeremiah 31:31-34; Ezekiel 36:24-28). In addition, the Bible prophesies a Messiah born to bring that restoration (Isaiah 9:6-7), set up an eternal Kingdom (Daniel 7:13-14), and judge all men and women one day (Daniel 12:2).

from the new testament

• Bibliography is built on passages such as 1 Timothy 3:16 which reads, “All Scripture is breathed out by God and profitable for teaching, for reproof, for correction, and for training in righteousness.” Because Scripture is breathed out by God, it has the same characteristics of God, meaning it cannot lie and does not error.
• Theology Proper, the study of the Father, is helped by the New Testament because of its clearer distinction of the three Persons of the Godhead. It teaches that the Father sent Jesus (John 3:16) out of love (1 John 4:1-11); He is just (Romans 3:26) and merciful (1 Peter 1:3).
• Christology is built heavily upon the New Testament. The New Testament teaches that Jesus is fully God (John 1:1) yet added on full humanity (Philippians 2:6). He, therefore, lived perfectly (1 Peter 2:22) yet also experienced everything that we experienced (Hebrews 4:15) without succumbing to sin (2 Corinthians 5:21). Because He was perfect, He died as a propitiation (Romans 3:25), that is, as a sacrifice that appeased God’s wrath. He did not stay dead and is in heaven now interceding for believers (Romans 8:34).
• Pneumatology, the study of the Holy Spirit, is also expanded in the New Testament. It teaches that the Spirit is fully God (Acts 5:3-4), is our helper (John 14:26), that He prays for us (Romans 8:26-27), produces fruit of righteousness (Galatians 5:22-23), and teaches us about Jesus (John 15:26).
• Soteriology, the study of salvation, comes to full realization in the New Testament. We learn that while salvation brings entry into heaven (John 14:2-3), it is primarily about being saved from God’s wrath against sinners (Romans 5:9) and is only available by believing in who Jesus is and what He did (John 3:16; Acts 16:31). Those who are truly saved cannot lose their salvation (John 10:28-29), but it is possible to be self-deceived, thinking one is saved while not actually being saved (Matthew 7:21-23).
• Hamartiology, the study of sin, is the reason salvation is needed. Its ongoing effects are revealed in the New Testament. All men and women are born corrupted by sin because of Adam’s sin (Romans 5:12) and have the punishment of eternal death hanging over them (Romans 6:23). Additionally, it’s not just men and women who are corrupted, but so is the rest of creation (Romans 8:20-22). Sin requires judgement and cannot be overlooked (Hebrews 9:27) but can be credited to another through a blood sacrifice (Hebrew 9:22).
• Anthropology, the study of humanity, is further clarified in the New Testament. We learn that all men and women sin (Romans 3:10-18) and are spiritually dead (Romans 3:23; Ephesians 3:1-3). Humans are created in the image of God and possess inherent dignity, yet this image is marred by sin, necessitating redemption (James 3:9; Colossians 3:10). Salvation only comes through Jesus. When saved, our nature is changed (2 Corinthians 5:17) and the Holy Spirit begins to reside in us (1 Corinthians 6:19) resulting in the production of good works (Ephesians 2:10).
• Angelology, the study of angels, gains additional information from the New Testament. We learn that angels protect (Hebrews 1:14) and bring heavenly news (Luke 2:10). They exist in incredible numbers (Revelation 5:11), with some praising God continuously (Revelation 4:8).
• Ecclesiology is the study of the church and is the one doctrine that is entirely from the New Testament. The New Testament reveals that the church began at Pentecost (Acts 2:1-4), was an unknown mystery prior to Jesus (Ephesians 3:4-6), consists of all Christians (1 Corinthians 12:13), and is expressed in localized gatherings (i.e., 1 Corinthians 1:2) where baptism, communion, and preaching are regularly practiced (Acts 2:41-42). All believers are expected to participate in their localized church gathering (Hebrews 10:24-25) for the purpose of serving other believers (1 Peter 4:10) and to become spiritually mature (Ephesians 4:11-13).
• Eschatology comes to a head in the New Testament. The Bible reveals that Jesus is returning (Acts 1:11) to rescue believers (1 Thessalonians 4:16-17) and to destroy the world (2 Peter 3:10), establishing His throne on earth for a thousand years (Revelation 20:7-9). Satan will stage one final coup to overthrow Him (Revelation 20:7-9) before being cast into Hell (Revelation 20:10). After that, all the dead will rise to face judgement (Revelation 20:12-13). Unbelievers will be judged for their rebellion and cast into Hell (Revelation 20:15) whereas believers will be judged for what they have done, either losing or gaining rewards (1 Corinthians 3:13-15). Through Jesus’ reign, the earth will be recreated and after all sinners have been removed, God will dwell on earth with His people (believers from both the Old and New Testaments) forever (Revelation 21:1-4).

implications for today

The Bible is not specifically a book of theology. Though it does contain direct teaching, it is largely a collection of historical events, poetry, and letters written about a specific time and to specific people. However, because it is all God-breathed (2 Timothy 3:16), everything in it is completely true. Theologians have collected what we either learn directly or infer by logical deduction and systematized it. Systematic theology is the result of that work.

How do the regular Christians benefit from these theological studies? First, we benefit from knowing everything that the Bible teaches about a topic to help guard us from error. Most historical errors about who God is, the Person of Jesus, and the nature of salvation have arisen by either elevating parts of Scripture over others or by trying to solve difficult questions that the Bible doesn’t solve. Systematic theology reminds us of everything the Bible teaches to guard us from arriving at conclusions from one passage that contradicts another.

It also helps us to learn deeply about key parts of Scripture. God did not simply dump a bunch of facts on humanity. Instead, over thousands of years He slowly revealed Himself and His plans. A systemized theology gathers together related portions of Scripture, helping us to focus on a particular topic, seeing how all of Scripture builds it in a specific, logical direction.

Finally, it reveals the logical and consistent mind of God. Systematic theology shows that all of scripture is speaking with a unified voice, never contradicting itself. It provides great confidence that God’s word really is God’s word.