You should perform your penance devoutly, that is to say, with reverence and with the sincere intention of giving up the sin. To say your penance reverently, my dear brethren, is to say it with attention to its spiritual importance and with devotion in your hearts. If you have said your penance with willful distractions, you will not have said it at all and you are obliged to say it again. To perform it devoutly is to perform it with a strong confidence that God will forgive you your sins through the merits of Jesus Christ, Who made satisfaction for us by His sufferings and His death on the Cross.
(from the Book “The Sermons of The Cure of Ars”, TAN Books 2013, Page 156)