Because these great blessings secured by Christ and offered through grace alone are signified in baptism—complete cleansing from unrighteousness, the renewal and fellowship of the Holy Spirit, access to God, and empowerment for service—we can say that baptism is a “visible gospel” illustrating the promises of God to all who believe. But this is the key point: just as OT Israel only received the promises and remained in God’s favor by faith that led to obedience, so too do only those undergo baptism receive the promises by faith. Circumcision represented a transformation of the heart that led one to love God and obey him (Deut. 10:16; 30:6; Ezek. 36:24-27). Those who received circumcision in their flesh alone were considered “uncircumcised” and rejected by God (Jer. 9:25-26; cf. Rom. 2:25-29), because this circumcision in body also pointed to the need for a circumcised heart. In the same way, we need to see baptism both pointing to our need for the renewal of our hearts and love for God, and also as a promise that he will graciously give us his Holy Spirit who will give us obedient love.
Just as the gospel message can be rejected in its verbal form—and this is certainly the fullest—it, too, can be rejected in its watery form. For those who are baptized but do not believe, baptism is a watery judgment like the flood in Noah’s day (1 Pet. 3:19-21). Likewise the Israelites were "baptized into Moses" at the Red Sea, yet many grumbled in discontent and fell into apostasy and sin and never reached the Promised Land (1 Cor. 10:1-5). This may be at root in the warnings in Hebrews 6 and 10; covenant members who were baptized and participated in the spiritual life of the church nonetheless took a path of disbelief and rejection of Christ, and so stand condemned. Like the foreskin of Israelites with uncircumcised hearts, so too unbelievers die in their own blood.
This ought to show clearly that reception of the covenant sign does not automatically ensure reception of the covenant promises; faith is always required by God. Those who trusted in their national heritage as Jews and circumcised “children of Abraham” but were filled with self-love and produced no fruit were shut out from the kingdom of heaven. So too will all baptized people who trust only in the sign of baptism and not the Person given therein will hear the words, “Away from me, you evildoers. I never knew you!”
But all that is to overlook the chief function of baptism in the NT. Peter’s main point is to emphasize the grace given to us, that “baptism now saves you . . . through the resurrection of Jesus Christ” (3:21). Jesus rose from the dead and secured eternal life for all who would trust in him and repent of their sins, seeking their righteousness in his fulfilled obedience alone and their forgiveness in his atoning death alone. In this way do all who “appeal to God for a good conscience” receive eternal life in his gracious favor.
Baptism thus ought to strengthen our faith by assuring us that we are in indeed washed clean from sin and made new in Christ. When the believer looks upon his baptism, he sees the gift of God in bringing him into his people as a “child of God” instead of leaving him out in the world as a “child of wrath” where Christ is not named, and he is thus assured of God’s fellowship. The believer sees that promised love and blessings came first, even when he was still a powerless infant or perhaps a new believer still weak in faith and strong in sin. Salvation is of God’s initiative and work, especially when viewed in terms of rebirth (no one gives birth to himself). And we see in baptism God’s gracious calling, to which we rightly respond with a clean conscience and full assurance of faith, having had our bodies washed with pure water (1 Pet. 3:21; Heb. 10:19-22). In baptism the believer sees and trusts the fact that the death of Christ was not withheld from him, but that he was plunged into this death, justified from sin, and consequently raised with him. The believer is assured that he has been reborn of the Holy Spirit, and that the Spirit makes him God’s son, secures his inheritance, and enables his sanctification. He is assured in baptism that he is set apart to God for priestly service—with priestly access! And, lest we forget that warnings are also blessings, we are guided by God in baptism to a knowledge both of sin we are to avoid and the faithful, rescuing Lord which we are to cling to.
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Of course, I've been continually referring to this assurance given to the believer. I'll ever stand by sola fide; and I trust you'll see the evidence of that here. The believer can know that God has given him all these blessings of purification from sin, forgiveness, access to his throne of grace, and the Counselor's fellowship and empowering for a life of love-and-holiness. How so? Because all of these are truly given to the believer. Everything pledged and portrayed in baptism is made good in the life of the believer--that is to say, in the lives of God's elect. Salvation is only for those whom he has foreknown, those who are beloved before time. (Do you get it now?) Hear these words of the Westminster Confession of Faith:
The efficacy of Baptism is not tied to that moment of time wherein it is administered; yet, notwithstanding, by the right use of this ordinance, the grace promised is not only offered, but really exhibited, and conferred, by the Holy Ghost, to such (whether of age or infants) as that grace belongeth unto [i.e., the elect], according to the counsel of God's own will, in his appointed time. (28.6, italics added)God does demand faith for the reception of his promises. In fact, salvation (the future sense before Christ's judgment seat) is contingent upon a faith that perseveres. But the beauty of God's grace is that everything he requires of us, this he himself provides freely, even repentance and faith. As the old song goes:
Come ye sinners, come and welcome,Let us praise him for his great grace and trust in it all the more!
God's free bounty glorify:
True belief and true repentance,
Every grace that brings you nigh.