Answer:
Repentance
Step-by-step explanation:
The "Good Thief" repents and admits his guilt and asks Jesus to remember him when he enters into His kingdom. The "Good Thief" showed that he still believed in and feared God despite his former lifestyle.
Jesus hears his repentance and promises the "Good Thief" that he will be with Him today in paradise. This shows again as Jesus said before that sinners can still enter into the kingdom of heaven. It also showed that He was able to forgive worldly sins as the Son of Man.
It also relates to a passage Jesus says to Thomas after the resurrection. Thomas refuses to believe until he can touch the wounds of Jesus. Jesus says to him you believe because you have seen me. Blessed are those who have not seen and yet still believe. As far as anyone knows, these thieves did not know of the miracles or the work of Jesus but yet one shows his belief.
It may also be connected to what Jesus says to Simon Peter when He asks Peter who he believes He is. Peter replies that He is the Christ, the Son of the living God. Jesus replied, "Blessed are you, Simon son of Jonah, for this was not revealed to you by man, but by my Father in heaven." One must also wonder if Jesus felt the same about this thief. As he hangs dying, he only asks that Jesus remember him but he adds "when you come into your kingdom. This man not only admits his guilt and agrees to the punishment he is getting but he also has indirectly is says he believes Jesus is who He says He is. Is this also why Jesus promises that he will be with Him in paradise? Did he recognize that this person not only admits his guilt but also has repented and shows a sign that he also believes he is in the presence of the Christ? Did He believe that this was also revealed to him by His Father in heaven?