I. The difference between the penitence and blasphemy of the two robbers is a type of the human race
That which we owe to your expectations, dearly-beloved, must be paid through the Lord's bountiful answer to your prayers that He Who has made you eager in the demanding would make us fit for the performing.
In speaking but lately of the Lord's Passion we reached the point in the Gospel story, where Pilate is said to have yielded to the Jews' wicked shouts that Jesus should be crucified. And so when all things had been accomplished, which the Godhead veiled in frail flesh permitted, Jesus Christ the Son of God was fixed to the cross which He had also been carrying, two robbers being similarly crucified, one on His right hand, and the other on the left: so that even in the incidents of the cross might be displayed that difference which in His judgment must be made in the case of all men; for the believing robber's faith was a type of those who are to be saved, and the blasphemer's wickedness prefigured those who are to be damned. Christ's Passion, therefore, contains the mystery of our salvation, and of the instrument which the iniquity of the Jews prepared for His punishment, the Redeemer's power has made for us the stepping-stone to glory: and that Passion the Lord Jesus so underwent for the salvation of all men that, while hanging there nailed to the wood, He entreated the Father's mercy for His murderers, and said, “Father, forgive them, for they know not what they do.”
Source: Sermons (New Advent)