@JudgeRightly explained it fairly clearly, but you never did. But JR wasn't quite getting
@Gary K's point (meaning Gary could have been clearer before getting his own panties in a wad). Here's his post:
His point was that the thief's application of salvation to himself (forgiveness of our sins and changes to our mindset based on that forgiveness, or sanctification), while recognizing he deserved his fate (confession of sins) and calling on Christ for mercy, demonstrates that justification is not by anything we can do, but purely on Christ's sacrifice on the cross.