Lets take a look at the thief on the cross. It is true that Jesus told the thief that he would be in paradise with him and I do not doubt that one bit. However, the thief on the cross cannot be used to show if baptism is necessary or not because the thief was under the old covenant and not the new covenant because Jesus had not died yet. Jesus was the mediator of a new and better covenant and it did not go into effect until he died (Heb. 8:6-7, Heb. 9:15-17). The new covenant made the old covenant obsolete (Heb. 8:13). In fact we are told the Jesus nailed the old law and its written requirements to the cross (Col. 2:14). So thief on the cross is not a new covenant example The only baptism the thief could have had was Johns baptism. We dont know for sure if the thief had been baptized with Johns baptism or not, but it was possible (Mat. 3: 5-6). But, one thing is for sure he could not be baptized into Christ because Christ had not died yet.
Now when Jesus did die and was resurrected notice what he commanded his disciples to do. Matthew 28:19 19 "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,
Mark 16:15-16 15 And He said to them, "Go into all the world and preach the gospel to every creature. 16 "He who believes and is baptized will be saved; but he who does not believe will be condemned.
Jesus made it clear that his disciples were to go teach the lost and baptize them. Now Mark account get very specific on how one is saved he said they must believe and be baptized. This goes hand and hand with what Jesus told Nicodemus "Most assuredly, I say to you, unless one is born of water and the Spirit, he cannot enter the kingdom of God. (John 3:5).
Now Acts 2 marks the beginning of the church. Peter preaches a lesson to those Jews that day that changed some of the lives forever. Some of them were pricked in the heart and they asked the apostles what they should do. Peter following the command of Jesus did not hesitate telling them what they needed to do to be saved.
Acts 2:38 38 Then Peter said to them, "Repent, and let every one of you be baptized in the name of Jesus Christ for the remission of sins; and you shall receive the gift of the Holy Spirit.
Please notice that Peter is telling the Jews that they must repent and be baptized for the remission of sins. We have seen so far that belief and baptism are equal with one another and repentance and baptism are equal with one another. Now notice what 3000 of those people did that day. Acts 2:41 41 Then those who gladly received his word were baptized; and that day about three thousand souls were added to them. So those who heard the word that day and accepted it were baptized and added to them. Vrs 46 tells us that it is God that adds us to his church and Paul tells us that it is at the point of baptism when God adds us to the church/body of Christ (1Cor. 12:13).
Now you gave Paul as an example of why baptism is not necessary for salvation. However, Paul talks a great deal about the subject of baptism and its importance. I have already given one example in 1Cor. 12:13. In trying to keep this brief I want to look at Pauls conversion because I believe that it teaches a very important message. His conversion is recorded in Acts 9, 22, and 26.
Acts 9:3-6 3 As he journeyed he came near Damascus, and suddenly a light shone around him from heaven. 4 Then he fell to the ground, and heard a voice saying to him, "Saul, Saul, why are you persecuting Me?" 5 And he said, "Who are You, Lord?" Then the Lord said, "I am Jesus, whom you are persecuting. It is hard for you to kick against the goads." 6 So he, trembling and astonished, said, "Lord, what do You want me to do?" Then the Lord said to him, "Arise and go into the city, and you will be told what you must do."
Here we see the Paul encounters Jesus and he wanted to know who he was. Paul had no doubt heard the sect he was trying to destroy talking about Jesus and Jesus is telling him it that it hard to kick against the truth. Paul was humbled in the site of the Lord and now he believed that this was Jesus and was trembling before him. Notice he ask Jesus what he wants him to do. Jesus tells him to go wait in the city for those very instructions.
Acts 9:8-9 8 Then Saul arose from the ground, and when his eyes were opened he saw no one. But they led him by the hand and brought him into Damascus. 9 And he was three days without sight, and neither ate nor drank.
Paul obeyed Jesus instruction and went to the city and he waited. Vrs 11 tells us that Paul was praying to God and that he had not ate or drank for 3 days. Now if anybody could have been saved by believing, repenting, praying, or confessing Jesus it would have been Paul. Had Paul entered into a saved condition having his sins removed at this point? To answer this lets look at this next verse in Pauls conversion.
Acts 22:12-16 12 "Then a certain Ananias, a devout man according to the law, having a good testimony with all the Jews who dwelt there, 13 "came to me; and he stood and said to me, 'Brother Saul, receive your sight.' And at that same hour I looked up at him. 14 "Then he said, 'The God of our fathers has chosen you that you should know His will, and see the Just One, and hear the voice of His mouth. 15 'For you will be His witness to all men of what you have seen and heard. 16 'And now why are you waiting? Arise and be baptized, and wash away your sins, calling on the name of the Lord.'
Ananias came and gave Paul the instructions he was waiting for and they were the same instructions that Peter gave in Acts 2. Notice he tells him to arize and be baptized and wash away your sins. Even though Paul had believed, confessed, repented and prayed he was not in saved condition he did not have his sins removed until he obeyed the instructions given by Ananias to be baptized. Again, we see the term baptized and the removal of sin tied together.
I want to show you some more examples of how Paul taught that one must be baptized to be saved. Please notice the following things that Paul states as being in Christ. 2Tim. 2:1 Grace 2Tim. 2:10 Salvation Eph. 1:3 Every spiritual blessing Eph. 1:7 Redemption and forgiveness of sin Rom. 8:1 No condemnation. Since all these things are found in Christ I think you would agree that we must be in Christ to be saved. Paul tells us how we get into Christ. Galatians 3:27 27 For as many of you as were baptized into Christ have put on Christ. Romans 6:3 3 Or do you not know that as many of us as were baptized into Christ Jesus were baptized into His death?
Paul makes it clear that one enters into Christ by being baptized. In fact when you read Romans 6: 1-11 and Col. 2:12-13 you will see Paul describes baptism as burial and the point that we are united with Christ in death having our old man crucified and having our sins forgiven.
Paul gives us yet another example of the importance of baptism. Paul teaches us that the church and Jesus body are one in the same (Eph. 1:22-23; Col. 1:18). He also teaches us that Jesus is a savior of that one body (Eph. 5:23). Again, I think that you would agree that we need to be in the church/body of Christ to be saved. Paul teaches that it is at the point of baptism that one enters into the church/body of Christ (1Cor. 12:13).