Since true repentance involves both sorrow for sin and faith in Christ,
God instituted baptism as a way of calling the lost to acknowledge
their sin and need of forgiveness while holding before them the promise
of forgiveness in Christ (Mark 1:8, Acts 2:38, Acts 22:16). However, if
you have grown up in a Christian home, the relationship between sorrow
for sin and faith in Christ might be so familiar to you that you fail
to see how important that insight is to a new convert.
Without the light of God's Word, the world at large sees no connection at all, between sorrow for sin and faith in Christ. In fact, the first reaction of those who see their sin for the first time is to try to "make up for that sin." And, they have no way of knowing that trying to "make up for their sin" is the opposite of what God wants (Proverbs 14:12). God wants them to look to Christ for mercy, yet they do the opposite. In fact, a cult member once told me that he thought that God would overlook his sins as long as he was trying to do what was right. He could not see that instead of trusting in Christ's sacrifice, he was trusting in his own "goodness" to bring forgiveness, and the Bible places all who trust in their own "goodness" under a curse (Jeremiah 17:5). [Luke 13:34, Romans 10:21]
When you analyze the reasoning of those who are in spiritual darkness, some of it is actually insane, yet without the light of God's Word they are blind to that fact. For example: The idea that someone can make up for a bad deed by doing a good deed is as ridiculous as a bank robber assuming that the banks he passes up make up for the ones he robs. Yet, most religions labor under that sort of reasoning, and cannot see that there is no forgiveness apart from faith in Christ (Hebrews 11:6).
Therefore, when Peter called upon his listeners to "repent, and be baptized… in the name of Jesus Christ for the remission of sins," he was using baptism to lead them away from works, while pointing them to Christ for forgiveness. In other words, he was saying, "don't try to make up for your sins, instead come to Christ for forgiveness and they will be washed away." Therefore, everyone who responded to Peter's words came to baptism confessing their sin and believing that their was forgiveness in Christ (Acts 2:38).
Consequently, when someone comes to baptism in response to the promise of forgiveness in Christ, his act of coming is actually a way of "calling on the name of the Lord" (Acts 22:16). In other words, he is simply requesting forgiveness by his actions rather than his words (Romans 10:13). And the ceremony gives him God's own pledge of a clean conscience (forgiveness) through the death burial and resurrection of Jesus Christ (1 Peter 3:21).
For that reason, the ceremony of baptism might be seen as a visual-aide that God has connected with the call to repentance, as a way of pointing the repentant to Christ. Through that ceremony God gives us the promise of forgiveness in Christ, through faith in Christ we have what is promised (Galatians 3:22, Romans 5:2).
Just as baptism was instituted as a way of pointing the repentant to forgiveness, the Lord's Supper was instituted for the same reason. One goes hand in hand with our initial repentance, while the other reminds us of our on going need for God's mercy. Moreover, as we hear the words that Christ spoke when He instituted His supper, we are reminded of the fact that His body was "broken" for us, and His blood "shed" for us "for the remission of sins," and that is the very essence of the gospel (1Corinthians 11:24, Matthew 26:28, Luke 22:19,20). For that reason, all who come to the Lord's Supper believing that Christ's body was "given" and his blood "shed" for them, receive the forgiveness that He died to secure for them (Mark 11:24). God uses the ceremony to give us His promise of forgiveness in Christ, and through faith in Christ we receive what is promised (Galatians 3:22).
At the same time, the Bible warns those who come of the danger of partaking unworthily, as a way of stressing the connection between repentance and Christ's death in our stead. In short, those who repent come to the Lord's Supper acknowledging their need for the forgiveness He died to obtain for them, the unrepentant come trusting in their own works to make them worthy (1 Corinthians 11:31).
Throughout history, the deceitfulness of the human heart has twisted and distorted the very means by which God offers us His mercy. Under the Old Covenant, the very sacrifices that were intended to emphasize the need for forgiveness, were twisted into works of righteousness (Hosea 6:6). And, there are many today that would twist baptism and the Lord's Supper into "acts of obedience" while being totally oblivious to the promise of forgiveness connected with those ceremonies. Therefore, we must stress the fact that while God uses the ceremony to give us the promise of his grace, it is only through personal faith in Christ that we receive what is promised (2Corinthians 1:20, Galatians 3:22).