If you only take the New Testament into account, it is difficult to understand the biblical nature of infant baptism. In fact, as Christians, we are called to be a two-testament church. We should understand our biblical theology by beginning at the beginning. When you begin at the beginning, you realize that, after God made all things good and through the sin of Adam, the world was plunged under God’s curse and wrath.When God made a covenant with Abraham, he promised to be a God not only to him, but also to his children.
He called Abraham and made a covenant with him to bless him and to bless all the families of the earth through him. When God made a covenant with Abraham, he promised to be a God not only to Abraham, the believer, but also to Abraham’s children. We see that promise to Abraham, the believer, and to his children repeated in every succeeding covenant that we have in Scripture. It is in the Mosaic covenant. It is in the Davidic covenant. It is even in the new covenant. If we look at Isaiah 44, Isaiah 59, and Jeremiah 32, we see that even in the new covenant, God’s promises to believers and their children are not revoked.
When Peter appears on the day of Pentecost and the outpouring of the Spirit has begun, he says, For the promises are to you and to your children and to as many as are far off, as many as the Lord our God will call.” We see that God has indeed kept his covenant promises and is confirming them in the new covenant through the gospel of Jesus Christ. Baptism is the sign and the seal of the covenant promises that belong to believers and that belong to the children of believers as well.