“The rite of confirmation is the solemn and joyous acknowledgment by the congregation that God has confirmed His covenant promise of salvation, which was signified and sealed to these baptized children, by granting them repentance and faith in our Lord Jesus Christ upon their coming to the age of understanding and commitment” (RCUS Directory of Worship).
God’s covenant promise of salvation is His promise to save His elect people through faith in Christ and to be their God and friend forever (Eph. 1:4-5). God says, “I will be your God and you shall be My people.”
When God saves His elect by granting them repentance and faith in Christ, He enters into a covenant of friendship with them, promising to be their God and the God of their descendants (Genesis 17:7). This means that God promises believing parents that they will have His elect among their descendants (Isaiah 59:21; Rom. 9:27), and that if they bring them up for Him, He will circumcise their hearts so they repent and believe in Christ (Gen. 18:19; Rom. 2:8-29; 2 Tim. 1:5). God commanded Abraham (an adult convert), and all the males of his household, including infants, to be circumcised, as a sign of God’s covenant promise to circumcise the hearts of His elect. “God will circumcise your heart and the heart of your descendants, to love the Lord your God with all your heart” (Deuteronomy 30:6).
In the NT, Baptism has replaced circumcision as the sign of God’s covenant of salvation with believers and their children (Acts 2:39; 1 Cor. 7:14). This is seen for example in the fact that Lydia (an adult convert like Abraham) believed, and then “she and her household were baptized” (Acts 16:15) – just as Abraham believed and then he and his household were circumcised. Therefore, “what circumcision was for the Jews, baptism is to our children” (Belgic Confession, article 34).
In the OT, covenant children were circumcised in infancy (as a sign of membership in the old covenant church); afterwards they were instructed in the true religion; and upon profession of faith in the Lord became full members of the church and were admitted to the Passover. This same basic pattern continues in the NT: covenant children are baptized in infancy (as a sign of membership in the new covenant church); then afterwards are taught the Christian faith, and then, upon profession of faith in Christ, become full members of the church and are admitted to the Lord’s Supper.
When God grants covenant children repentance and faith in Jesus Christ, He is confirming His covenant promise of salvation (Rom. 15:8; Gal. 3:17). “It does not matter when the Holy Spirit placed faith in the covenant youth’s heart; if his parents and the church have done their work responsibly, he has from childhood known the teaching of God’s Word. But God is the one who has given this faith. He has confirmed the promises of His covenant. By the rite of Confirmation, the church is recognizing what God has confirmed by means of the young person’s response of faith” (Maynard Koerner, Pastoral Ministry from a Covenantal Perspective).