Baptism, the sign of membership in Christ's Church, is more than a sign; it is an absolute necessity. "Unless a man is born of water and the Spirit, he cannot enter the kingdom of God," were Christ's words to Nicodemus (John 3:5). The importance of Baptism was stressed above all by our Lord's first priests and Bishops, the leaders of the Church, the Apostles. "Get up and have yourself baptized and your sins washed away," were almost the first words that Paul the Apostle was to hear in his new- found Christian faith (Acts 22:16). And it is Paul who has best of all expressed the traditional Christian faith in the power of this sacrament (Rom 6:3-11).
Baptism puts us in union with Christ, causes us to share His life, to the extent that His death is our own and His resurrection ours. We are dead to sin, alive to the life of God. We are new persons. It is no wonder that St. Peter says simply, ~Baptism ... saves you" (1 Pet 3:21).
This does not mean, of course, that Baptism is an automatic guarantee of salvation. God saves man without destroying man's freedom. There is no such thing as an absolute, infallible certainty of salvation during this life, because at any time man has it in his power to turn his back on God and reject Him.
Christ knew that the members of His Church would sin, and thereby break the bond that had united them to Him in Baptism. Such was the divine mercy that God would not permit this bond to be broken forever, and to assure this, He provided another channel of grace. When a person has committed sin, he has a sure way to return to the salvation of Christ, through the sacrament of Penance.
The matter of this sacrament is the sorrowful confession of one's sins to Christ's minister. The form is the words of absolution, uttered by the priest of the Church in the name of Christ. This sacramental sign of confession and forgiveness is more than a symbol; it is the true absolution given the sinner by Christ Himself.
Why is confession to a mere human being necessary? Why cannot the sinner simply go to God directly and obtain forgiveness? Because God has determined that it is through confession to His priest and absolution given by the same priest that He will forgive our sins. We do not decide for ourselves how we shall obtain forgiveness, any more than we decide for ourselves how we shall obtain Christ's salvation in the first place. If the priest can act for God in the matter of Baptism, which cleanses us of sin, why should we doubt his commission from God to transmit forgiveness of sin through the equally valid Christ-instituted sacrament of Penance.