Your question deals with one of the most important, yet debatable, issues within the Christian family. We receive many wonderful gifts through baptism, but the most important role of baptism is to identify us with Jesus and with other believers who follow him. Baptism is our profession of faith.
This is why the first Christians declared their faith in Christ at baptism by saying, "Jesus is Lord." The Apostles' Creed and other statements of faith were also associated with baptism. Baptism involved more than correct belief, though. It was an induction into a new way of life. It signaled a lifelong process of learning and living according to the gospel of Christ.
During the Reformation, Huldrych Zwingli compared baptism to the white cross sewn onto the uniform of a Swiss soldier (we see this same symbol on the Swiss flag today). Combatants bearing this symbol identified with the Swiss cause. Just so, baptism marks us off as militia christi, soldiers of Christ who wield the spiritual weapons Paul described in Ephesians 6.
Second, baptism is closely related to personal faith and repentance. This is the primary reason why many Christians (and I am among them) think baptism should be administered only to those persons who have repented of their sins and believed the gospel. Baptism may confirm the faith of believers, but it does not create faith in those who have never trusted in Christ.
Yes, God's covenant of grace is broader than baptism and may well embrace those who have not yet come to personal faith in Christ, such as infants, young children, and the mentally incompetent, among others. Still, like the Lord's Supper, baptism signifies an earnest pledging of ourselves to God (1 ...1