33 And when they were come to the place which is called Calvary, they crucified him there; and the robbers, one on the right hand, and the other on the left. 34 And Jesus said: Father, forgive them, for they know not what they do.
Chrysostom: Because the Lord had said, Pray for them that persecute you [Matt 5:44], this likewise He did, when He ascended the cross, . . . not that He was not able Himself to pardon them, but that He might teach us to pray for our persecutors, not only in word, but in deed also. But He says, Forgive them, if they should repent. For He is gracious to the penitent, if they are willing after so great wickedness to wash away their guilt by faith.
Bede: He prayed not for those who chose rather to crucify, than to confess Him whom they knew to be the Son of God, but for such as were ignorant what they did, having a zeal for God, but not according to knowledge.
Greek Expositor: For those who after the crucifixion remain in unbelief, no one can suppose that they are excused by ignorance, because of the notable miracles that with aloud voice proclaimed Him to be the Son of God.
Scripture from the Douay-Rheims Bible. Commentary from St. Thomas Aquinas, Catena Aurea, Vol. III (London: Rivington, 1843).