Thief on the Cross

Invariably, when you talk to someone who reject water immersion is necessary for salvation, they will ask the question: "What about the thief on the cross?"
It must be noted that the question is asked in an attempt to get out of doing what the Bible explicitly states is necessary to do to be saved. That aside, I want to address why the thief on the cross is not a valid objection to water immersion into Christ for the remission of sins.
== Wrong Covenant ==
The first reason that the thief on the cross is not a valid objection to water immersion is that he was saved under the Old Covenant not the New. Water immersion is a requirement for salvation under the New Testament so bringing up someone who was saved under the Old Testament is not relevant. When the thief was hanging on the cross and Jesus saves him by saying 'today you will be with me in Paradise', Jesus was still alive and able to speak. The New Covenant did not go into effect until the death of the testator (Heb 9:15-17). Note what verse 17 says: "For a testament is of force after men are dead: otherwise it is of no strength at all while the testator liveth." Christ still lived and so the command to be baptized into the death, burial, and resurrection of Jesus Christ for the remission of sins was not in effect yet.
Appealing to someone who was counted righteous under the Old Covenant is an attempt to appeal to the Old Covenant itself for justification which Paul states means you are not under grace (Galatians 5:1-4). Everyone who appeals to the thief on the cross is therefore rejecting grace for salvation and trying to be saved by some other means.
== Wrong Purpose ==
Very close to the above reason is the idea that baptism in the New Covenant is into the death, burial, and resurrection of Jesus Christ. As Romans 6 vividly describes, when we go down into the water, we are buried with Christ as Christ was buried. And when we come up out of the water we are resurrected to new life as Jesus was resurrected when He came up out of the grave. Since this had not yet happened to Jesus, it would have been impossible for the thief to have been baptized into the death, burial, and resurrection of Christ. It is in His death that Jesus shed His blood and so it is in His death that we must contact it. If we are baptized into His death as Paul says in Romans 6 (and John alludes to in 1 John 5:6,8) then it is in baptism that we contact the blood of Christ. Christ had not shed His blood in death (the spear being thrust into His side) so the thief did not have access to that yet, even if he could climb down off that cross and go get baptized.
== Wrong Circumstance ==
It is evident that Jesus had the power to forgive sins while on Earth (Matthew 9:6). While hanging there with the thief who recognized and acknowledged Jesus, Jesus had the power to forgive his sins. It is a relatively unique circumstance that only two people in history have ever literally physically been in. No one else had ever been or ever would be in that circumstance again. So to appeal to this very unique circumstance as evidence of what is normal in regard to salvation is absurd. Unless you find yourself hanging next to Jesus on a cross around 33 AD, these circumstances don't apply to you.
== Conclusion ==
Rather than looking for a way out of doing what Christ has commanded us to do, people ought to be looking at what Christ said to do under the New Covenant and say "I want to do that for the reasons Jesus said I should do them." Jesus was very explicit when He said that he that believes the gospel and is immersed shall be saved in Mark 16:16. Through the Apostles and other inspired writers we learn the purpose of water immersion and what transpires when we are immersed. We are immersed into His death, burial, and resurrection and come into contact with His blood as noted above. We put on Christ (Gal 3:26-27). Our sins are remitted (Acts 2:38) washed away (Acts 22:16). We are sanctified and cleansed (Ephesians 5:26). The body of sins is cut away (Colossians 2:11-13). We are saved (1 Peter 3:21).
In Truth and Love.