Specifically, baptism is a sign and seal of the benefits of forgiveness (Acts 2:38 and 22:16) and of regeneration (Titus 3:5), a being incorporated into the fellowship with Christ and His Church (Rom. 6:4). Therefore baptism is ministered not only to such adults as have been won for Christ through the work of missions, but to the children of believers also, for they together with their parents are included in the covenant of grace, belong to the church (1 Cor. 7:14), and have been taken up into fellowship with the Lord. And when these children grow up, and by public confession personally acquiesce in that covenant, and have come to the years of discretion, and can distinguish the body and blood of the Lord (1 Cor. 11:28), then they are called together with the whole church again and again to proclaim the Lord’s death till He come, and so strengthen themselves in the fellowship with Christ. For, although baptism and the holy supper have the same covenant of grace as their content, and although both give assurance of the benefit of the forgiveness of sins, the holy supper differs from baptism in this regard that it is a sign and a seal, not of incorporation into but of the maturation and strengthening in the fellowship of Christ and all His members (1 Cor. 10:16:17).

Herman Bavinck, Our Reasonable Faith: A Survey of Christian Doctrine, trans. Henry Zylstra (Eugene, OR: Wipf and Stock, 2002), 541-542. Translation of Magnalia Dei (1909).

Those two sacraments have the whole covenant of grace with all of its benefits, in other words, they have Christ Himself as their content, and accordingly they cannot convey those benefits except by the way of faith. They were, accordingly, instituted for the believers and assure these believers of their portion in Christ. They do not precede the Word but follow it; they have not the power to grant a particular grace which cannot be given by the Word nor be accepted by faith; rather, they are based on the institution of the covenant of grace on God’s part and the confirmation of that covenant of man’s part.

Herman Bavinck, Our Reasonable Faith: A Survey of Christian Doctrine, trans. Henry Zylstra (Eugene, OR: Wipf and Stock, 2002), 541. Translation of Magnalia Dei (1909).