What does Mark 14:72 mean?
Peter's interaction with Jesus after the Passover meal in the upper room is characterized by threes. Peter promises Jesus three things: he will not fall away from Jesus (Mark 14:29), he would follow Jesus into prison (Luke 22:33), and he would rather die than deny Jesus (Mark 14:31). Three times, Jesus tells Peter to stay awake, watch, and pray that he does not fall into temptation—that Peter would be able to fulfill his oaths. Three times, Peter falls asleep, instead (Mark 14:32–41). Now, empty of his prior resolve, unprepared for spiritual warfare, and fearful because of his own crime, Peter denies Jesus three times (Mark 14:66–72).In the dark of the garden of Gethsemane, surrounded by his compatriots, Peter was brave and rash enough to draw his sword against the priests' servants (John 18:10). In the light of a fire, in earshot of the guards beating Jesus (Mark 14:65), and guilty of his own sin, Peter folds. The group of accusing servants includes a relative of Malchus, the man Peter assaulted (John 18:26). Peter is afraid of being punished for his crime while Jesus is being punished without reason.
Peter addresses this dichotomy later in his first epistle (1 Peter 2:18–25). He describes Jesus when he says, "For this is a gracious thing, when, mindful of God, one endures sorrows while suffering unjustly" (1 Peter 2:19). He then says that it is of no account if you sin and are punished for it. You deserve the punishment. Peter lied under an oath he called upon himself while there was no deceit found in Jesus' mouth. While Peter hid, Jesus "bore our sins on his body on the tree, that we might die to sin and live to righteousness" (1 Peter 2:24).
The passage in 1 Peter is undoubtedly informed by Peter's passionate mourning, here. All of Peter's grandstanding is swept away. Luke says that at this point, Jesus literally turns and looks at Peter (Luke 22:61). In fear for his safety, Peter has forgotten Jesus' warning to him. He finally realizes that all his bravado and claims and presumptions mean nothing. With that dramatic, soul-crushing locking of eyes, Peter realizes exactly what he has done, and just how unworthy he is of Jesus.
The Greek phrase describing Peter's reaction here is epibalōn eklaien. These words, respectively, refer to "falling, crashing, casting, or laying down," and "weeping, as in ritual mourning." Peter literally collapses to the ground in agony, wailing and sobbing over his denial of Christ.
But the final triptych is yet to come (John 21:15–18). After the resurrection, on the shore of the Sea of Galilee, near where Jesus first asked Peter to be His disciple (Mark 1:16–18), Jesus will ask Peter three times if Peter loves Him. Three times, Peter readily admits he has phileo for Jesus; that is, he loves Jesus dearly. In his humility, he admits he does not have agape love for Jesus; he is not able, in himself, to pick up his cross and follow Him (Mark 8:34). It is here that he finally becomes open to Jesus' work in his heart so that Peter can, ultimately, follow Jesus to his death.