Father Girardey cites the example of St. Peter to demonstrate why even a virtuous person needs to pray.
He says: “St. Peter truly loved our divine Saviour, and probably with a greater love than any of the other apostles. And nevertheless he basely denied his Divine Master three times, and not only did he deny Him, but even swore with fearful imprecations that he did not know Him. How did he happen to fall so low, so deeply? It was because he had neglected to pray.”
Father Girardey, in recounting the story of the arrest of Jesus (Mk 14), shows how this came to pass. He writes: “After the Last Supper Jesus betook Himself with His apostles to the Mount of Olives. ‘Jesus saith to them: You will all be scandalized in My regard this night, for it is written: I will strike the shepherd and the sheep shall be dispersed. . . . But Peter saith to Him: Although all shall be scandalized in Thee, yet not I. And Jesus saith to him: Amen I say to thee, to-day, even in this night, before the cock crow twice, thou shalt deny Me thrice. But Peter spoke the more vehemently: Although I should die together with Thee, I will not deny Thee.’ Then Jesus left eight of the apostles at the entrance of the garden of olives, and took with Him Sts. Peter, James and John and ‘saith to them: My soul is sorrowful even unto death, stay you here and watch.’ Then Jesus went forward a little to pray. . . . Then He came to the three apostles, ‘and findeth them sleeping. And He saith to Peter: Simon, sleepest thou? Couldst thou not watch one hour? Watch ye and pray that you enter not into temptation. The spirit indeed is willing, but the flesh is weak.’ Far from performing this injunction, St. Peter continued to sleep and did not pray. He was tired, and saw no necessity for praying, for was not his mind made up to stand faithfully by Jesus? Hence when the time of trial came, he was left to his weakness. When Judas came with the armed multitude to arrest Jesus, Peter at first showed his bravery by striking with the sword; but as Jesus soon after allowed Himself to be arrested, bound and led away, Peter took to flight, just like the other apostles.”
“Had Peter obeyed the injunction of his divine Master, he would not have so shamefully fallen and denied Him, for his prayer would have obtained for him the grace and strength to remain true and steadfast.”
Quotations from Ferreol Girardey, Prayer: Its Necessity, Its Power, Its Conditions (St. Louis: B. Herder, 1916).