The new covenant is the covenant which our Lord Jesus Christ has inaugurated by his life, death, resurrection, and glorious exaltation to the right hand of God. It must be viewed as the culminating covenant in the sense that all of the previous covenants have been leading to it and anticipating it, in a variety of ways. Like the other covenants, it is part of the one plan of the Triune God to save a people for himself, but viewed vis-à-vis the previous covenants, it is the covenant which has now brought to fulfillment all that God promised and all that the OT anticipated and longed for, all the way back to the initial promise of Genesis 3:15.And:
Baptism signifies a believer’s union with Christ, by grace through faith, and all the benefits that result from that union. It testifies and announces that one has entered into the realities of the new covenant and as such, has experienced regeneration, the gift and down-payment of the Spirit, and the forgiveness of sin. It graphically signifies that a believer is now a member of the body of Christ (Eph. 4:22-25). It is our defining mark of belonging as well as a demarcation from the world. It signifies entry into the eschatological order of the new creation—that which our Lord Jesus Christ has ushered in. In all of these ways, baptism is a beautiful God-given rite which displays, proclaims, and testifies to the reality of the gospel.Also see the recent book to which Wellum contributed—Believer’s Baptism: Sign of the New Covenant in Christ, ed. Thomas Schreiner and Shawn Wright. His chapter is available online for free.