Adam Clarke's Commentary on the Bible

Verse 34 (Luke 23:34)

They know not what they do - If ignorance do not excuse a crime, it at least diminishes the atrocity of it. However, these persons well knew that they were crucifying an innocent man; but they did not know that, by this act of theirs, they were bringing down on themselves and on their country the heaviest judgments of God. In the prayer, Father, forgive them! that word of prophecy was fulfilled, He made intercession for the transgressors, Isaiah 53:12 .

- Adam Clarke's Commentary on the Bible