St. John Vianney
“We must, before going to the Holy Table, be sure that we have spent sufficient time in examination of conscience in order to discover our mortal sins, and that we have a great sorrow also, that our confession has thus been entire. We must have a firm determination to do, by the grace of God, all that we can, not to fall into sin again. If we have not confessed entirely or sincerely, in receiving Holy Communion we would put Jesus Christ at the feet of the devil. What an enormity!”
Source: St. John Vianney, The Meditations of the Curé D’Ars