ESV - 16 Whoever believes and is baptized will be saved, but whoever does not believe will be condemned.
For follow-up discussion and general commentary on the topic. Comments are sorted chronologically.
I think the confusion starts with the following two parts of John
John 3:5 Jesus answered, "Truly, truly, I say to you, unless one is born of water and the Spirit, he cannot enter the kingdom of God.
John 3:16 "For God so loved the world, 9 that he gave his only Son, that whoever believes in him should not perish but have eternal life. 17 For God did not send his Son into the world to condemn the world, but in order that the world might be saved through him. 18 Whoever believes in him is not condemned, but whoever does not believe is condemned already, because he has not believed in the name of the only Son of God.
The two thieves highlight an interesting point, the one Jesus said would be in paradise was the one that asked Jesus to remember him when meets with God - in other words such a request shows that this thief believed/had faith in Jesus. The other criminal -not so much. Im just assuming here (personal opinion), that the belief and acceptance in Christ as the Son of God before death is the important point because there's not much else they could do on the cross. The Baptism portion is important for those who have come to find Christ/change their lives/be saved, and have years ahead that the cleansing from the old (water) and guidance going forward (Holy Spirit) that from there on you can help others that are lost/looking to be saved ie Gods work through you. Like I said that's just my thought, I haven't been Baptized yet, I just want to understand it fully first.
Was the thief on the cross water baptised on the day of the Lords cruxifiction when he pronounced "this day you with be with me in paradise?
You know the answer!
In my opinion, you can not use the thief on the cross as Christ had not yet died for our sins and been raised up. He had the authority to forgive the thief's sins as he did for others.