I know of no scripture which makes baptism a condition for participating in the Lord Supper. Having said that, there are scriptures which would IMPLY that one should be baptized as soon as they are saved and thus the norm would be that one has been baptized when coming to the Lord’s Supper.

Let’s read Acts 10:43-48 from the New King James Version: “To Him all the prophets witness that, through His name, whoever believes in Him will receive remission of sins. While Peter was still speaking these words, the Holy Spirit fell upon all those who heard the word. And those of the circumcision who believed were astonished, as many as came with Peter, because the gift of the Holy Spirit had been poured out on the Gentiles also. For they heard them speak with tongues and magnify God. Then Peter answered, ‘Can anyone forbid water, that these should not be baptized who have received the Holy Spirit just as we have?’ And he COMMANDED THEM TO BE BAPTIZED in the name of the Lord.”

We believe this is the proper order for the church age in which we live. One hears the gospel, believes it, and is baptized. This was the order that Peter followed from the very beginning as we see in Acts 2:41, “Then those who gladly received his word were baptized.” And this was the order practiced by the Apostle Paul on his missionary journeys, as illustrated in his gospel outreach in Corinth. “Then Crispus, the ruler of the synagogue, believed on the Lord with all his household. And many of the Corinthians, hearing, believed and were baptized.” (Acts 18:8)

I can imagine Peter thinking (after he saw the evidence of salvation and the receiving of the Holy Spirit), “Ah, these people have been saved and baptized by the Spirit into the body of Christ. Now let’s baptize them with water and make them disciples of Christ.” Peter had received this commission to make disciples in Matthew 28:19-20, “Go therefore and MAKE DISCIPLES of all the nations, BAPTIZING THEM in the name of the Father and of the Son and of the Holy Spirit, TEACHING THEM to observe all things that I have commanded you.” He knew that in order for men to willingly submit to becoming disciples, they would have to be true believers, so having seen the evidence of faith in Christ in Cornelius and those with him, he immediately “commanded them to be baptized.” Notice, he did not wait for them to be exercised or to fully understand what baptism means. Instead he took the initiative (based on Matthew 28:19-20) and baptized them. He no doubt told them that their baptism would make them an official disciple of Christ and in time he would teach them the full significance of baptism.

If your friend has truly received Christ as his personal savior and is a member of the church through the baptism of the Holy Spirit, he should surely be willing to submit to water baptism in order to publicly take his place as a disciple (i.e. follower) of Christ. Of course, he should also desire to respond to the Lord’s request, “This, do, in remembrance of Me” by participating in the Lord’s Supper.

I would only add that we need to remember that baptism and the Lord’s Supper have NOTHING to do with salvation, for we saw that it is through faith in Christ and His work on the cross that brings salvation and the forgiveness of sins. Baptism and the Lord’s Supper are both PICTURES of Christ’s death for the believer. In baptism the disciple realizes that through Christ’s death he is looked upon as having been “buried with Christ” and can now walk in “newness of life” (see Romans 6:3). In the Lord’s Supper we have the symbols of Christ’s BODY and BLOOD in the BREAD and the WINE, reminding us that He was willing to become a man in order to lay down His life and to shed His blood so we could be forgiven. (318.3) (DO)