The Bible is a unified storybook. Yet many today want to divide it into two different stories with two different peoples. This theology, known as dispensationalism, sees strong discontinuity between Old Testament Israel and the New Testament church. (This view is often associated with premillennialism and the rapture.) Now it does not help that our English Bible is divided into two “testaments” (another word for “covenant”), making it sound like the Old Testament was for prior times and the New Testament is for today. Nothing could be further from the truth.
The New Testament is built on the foundation of the Old Testament. In fact, Jesus and the Apostles only had the Old Testament when they were preaching and ministering. Their words and writings ended up forming the New Testament, which is full of quotations from the Old Testament. And they treated these passages as binding on Christians. That’s why they cite things like the 5th commandment and tell Christians to obey it (Matthew 15:4; Ephesians 6:4).
Jesus and the Abrahamic Covenant
All of this is to say that the Bible is a unified whole with strong continuity between the Old and New Testaments. The Bible is the story of God saving His people from sin and judgment—one people, not two. God called a man named Abram (later changed to Abraham) to be the father of “a multitude of nations” (Genesis 17:4). God gave Abraham land and offspring, and it was said that “in [him] all the families of the earth shall be blessed” (Genesis 12:3).
Abraham’s descendants (through Isaac)—as well as others who came to believe in the God of Abraham (e.g. Rahab, Ruth)—formed the nation of Israel. From this line came the Lord Jesus Christ (Matthew 1). Jesus is said to be the “offspring” of Abraham (Galatians 3:16), and it is in Him that all God’s promises find fulfillment. God’s promise of offspring found partial fulfillment in the people of Israel, but it finds ultimate fulfillment in Christ and all those who believe in Him (Romans 4:16). God’s promise of land found partial fulfillment in Israel taking the land of Canaan (1 Kings 4:20-21), but it finds ultimate fulfillment in Christ’s kingdom stretching throughout the whole world (Rom 4:13). Christ has authority over all the earth (Matthew 28:18) and He is redeeming people from every tribe, language, people, and nation (Revelation 5:9). The Bible—Old Testament and New—is all about Jesus.
Jesus is the second Adam, the offspring of Abraham, the lion of the tribe of Judah, the greater Moses, our Great High Priest, the true temple, the son of David, and the King of Israel. And all who believe in Jesus are the children of Abraham (Galatians 3:7) who inherit the promises made to Abraham (Galatians 3:14, 29). Jews and Gentiles came together in faith in Christ as “one” people, breaking down “the dividing wall of hostility” (Ephesians 2:14). Believing Gentiles have been grafted in to the olive tree of salvation, and unbelieving Jews have been cut off (Romans 11:17-24).
The Covenant of Grace
This is God’s covenant of grace. God made one overarching covenant with His people that finds expression in several specific covenants in Scripture, including the Abrahamic (Genesis 15:1-21, 17:1-27), Mosaic (Exodus 19–24), Davidic (2 Samuel 7:8-17), and new covenants (Jeremiah 31:31-34). The covenant of grace is God’s continuous promise to redeem his people—“to be God to you and to your offspring after you” (Genesis 17:7). The new covenant cannot be understood as something detached from the previous covenants. Rather, it builds on them. This is seen in that the new covenant was initially made "with the house of Israel and the house of Judah” (Jeremiah 31:31) and now applies to the church (Hebrews 8:8).
This is covenant theology. And it is a beautiful thing. It unifies the Bible and helps make sense of it all.
That is why you should study it. Of course, there are debates within covenant theology that will stretch your understanding of Scripture (e.g. the role of the Mosaic covenant). But covenant theology also deals with very practical questions—Should I baptize my baby? Should I support the modern nation-state of Israel? Should I keep the Sabbath? How should I regard Old Testament commands?
I could write for days on these subjects, and you can comment below if you want more information. But for now let me recommend some resources that can help you in your study of covenant theology. Most of these resources are aimed at adults, but they can also be utilized by high school students seeking to learn more about the Bible and theology.
Resources for Covenant Theology
R.C. Sproul teaches a course on covenant theology at Ligonier Ministries. You can purchase the entire course for around $20, or you can subscribe to all Ligonier’s videos for $9 per month. You can sample some of them on Ligonier or try to find them on YouTube. Reformed Theological Seminary also offers two different audio courses on covenant theology at RTS iTunes (here and here). You can listen to them in your car. Both of them are free.
Whether or not you listen to a course, you will definitely want to read some books on covenant theology. The best introductory book on covenant theology is Covenants Made Simple by Jonty Rhodes. The book is not perfect. Covenant theology involves tons of controversial issues, so one is bound to disagree with someone on something. For example, I think Rhodes’ definition of a covenant leaves out the fact that all biblical covenants involve oath-signs (though he still identifies many of these signs, such as baptism as the sign of the new covenant). But this book is still a great introduction.
If you want a more technical discussion of covenant theology, I recommend Covenant Theology by Peter Golding. He gets into the details of different views throughout history of the covenant of works and the Mosaic covenant. This is very helpful. A famous book on covenant theology that I must also mention is Christ of the Covenants by O. Palmer Robertson. I like this book, but it is not the first thing I would recommend on the subject.
Covenant Theology and Baptism
If you delve enough into covenant theology, you will eventually get into the issue of infant baptism. Ultimately, the question of infant baptism deals with the place of children in the church. Your take on the place of children in the church is a good measure of how much continuity you see between God’s dealings with people in the Old and New Testaments. Reformed covenant theology has regarded children as members of the church because they are part of the household of their parents and thus part of God's covenant. This was certainly the case in the Old Testament, as children were members of the Abrahamic covenant (Genesis 17:12).
Reformed covenant theology argues that the children of Christians are also to receive the covenant sign (baptism) as a mark that they are members of the covenant. The new covenant is a renewal of the Abrahamic covenant (Galatians 3), baptism has replaced circumcision as the covenant sign (Colossians 2:11-12), and children are nowhere put out of the covenant. In fact, there are several examples of whole households being baptized (Acts 11:14; 16:14-15, 30-34; 18:8; 1 Corinthians 1:16), which alludes to the covenantal language of Genesis 17:23, 27 [LXX]. In other words, God still deals with families as a unit (Ephesians 6:1-4). Of course, children still need to embrace Christ through faith, but this faith is not seen as a prerequisite for baptism. Here are some good books to look into the issue from both sides.
The Case for Covenantal Infant Baptism edited by Gregg Strawbridge. This is a collection of essays from a Reformed covenantal view. They cover a variety of issues within covenant theology and are very informative. I consider this to be the premier work on covenantal infant baptism.
Baptism: Three Views edited by David Wright. This book has a good debate between Sinclair Ferguson and Bruce Ware. I would disregard the dual practice view and focus on Ferguson and Ware’s chapters. This is probably the best short treatment of both sides of the baptism debate.
Kingdom Through Covenant by Peter Gentry and Stephen Wellum. This is a long work that makes the case for what is known as “Progressive Covenantalism” (similar to New Covenant Theology). This is an attempted via media between traditional covenant theology and dispensationalism. In other words, the authors argue for less continuity than traditional covenant theology and reject infant baptism. They have written a shorter version titled God’s Kingdom Through God’s Covenant. I disagree with some of their conclusions, but I will leave that to the reader.