He who corresponds with grace will be saved, while he who resists grace will be lost. This important truth is illustrated by the conduct of the two thieves, in the same way that it is illustrated by the conversion of St. Peter and the despair of Judas. The thief on the left hand received quite as much grace as did the other, for Jesus prayed for both, and shed His Precious Blood for both. He saw the patience and love of Jesus as well as the other, but he resisted grace, hardened his heart, and thus died in his sins, and was eternally lost. On the contrary, the thief on the right hand corresponded with grace and was thereby saved. He left the cross for paradise, whereas the other left it for hell.
[From 'A Practical Commentary on Holy Scripture' by Bishop Knecht, D.D.]
(1899 Douay-Rheims Bible)