Who blasphemed the Lord during His crucifixion, the thief on the left or the thief on the right? How could it he that one deserved Paradise?
In the beginning both thieves blasphemed the Lord.
St. Matthew the Evangelist said “Even the robbers who were crucified with Him reviled Him with the same thing.” (Matt. 27:44) And St. Mark also said “And those who were crucified with Him reviled Him.” (Mark 15:32)
St. Luke is the one who mentioned the faith of the thief on the Lord’s right hand saying ” Then one of the criminals who were hanged blasphemed Him, saying, “If You are the Christ, save Yourself and us.” But the other, answering, rebuked him, saying, “Do you not even fear God, seeing you are under the same condemnation? “And we indeed justly, for we receive the due reward of our deeds; but this Man has done nothing wrong.” Then he said to Jesus, “Lord, remember me when You come into Your kingdom” (Luke 23:39-42).
Probably it was the miracles that happened during the time of crucifixion that changed the heart of the thief on the right.
When he saw the earth quake, the rocks split, and the heavens darken, his heart was touched as he was touched by Christ’s forgiveness of those who crucified him and His prayers on their behalf. So he stopped reviling and blaspheming. He believed and defended the Lord Christ, admonishing the other thief. He declared his faith to the Lord asking to be remembered, and received the promise of Paradise.