When Jesus spoke of this to the thief, he is referring to the same promise God gave to Abraham (Genesis 22:17-18) Not the kind of paradise that is found on earth but is found in heaven. His Words are hope for all of us sinners. Showing how merciful our God is in this specific event in the Bible is a reminder that despite our grievous sins, we only need to have a repentant heart to receive hope (believe the words of Jesus) and the promise of salvation. The good thief believed so he immediately received his reward. This is a picture of encouragement to all of us, a promise of Paradise.