What about the thief on the cross?

What about the thief on the cross?
BQ: A common objection to what the Bible says about being immersed/baptized is, "What about the thief on the cross? He wasn't baptized, but Jesus said he was saved." How can this be?

A: Before Jesus died, the Old Testament/Covenant/Will was still in effect. Hebrews 9:15-17 explains "For this reason He is the mediator of a new covenant, so that, since a death has taken place for the redemption of the transgressions that were committed under the first covenant, those who have been called may receive the promise of the eternal inheritance. For where a covenant is, there must of necessity be the death of the one who made it. For a covenant is valid only when men are dead, for it is never in force while the one who made it lives. Therefore even the first covenant was not inaugurated without blood."

Jesus hadn't yet died, but he had full power over his last will and covenant.  “And Jesus came and spoke to them, saying, "All authority has been given to Me in heaven and on earth.” (Mt 28:18) 

Imagine that you you're planning out your will. You have $500. While you're still alive, being the owner of the will, you can still give away money (salvation) as you see fit to anyone you think deserves it. After you're dead, as the Bible points out, the will is then in effect, and the money (salvation) is only given out as stipulated. For these reasons, the thief on the cross is not a valid example of New Testament salvation. 
(PN155)