In the wee hours of Thursday morning while Jesus was being interrogated by Caiaphas and his yes-men from the Sanhedrin, Peter was facing his own interrogation of sorts by the servants and officers gathered in the courtyard of the high priest’s palace. But whereas Jesus, strengthened by His prayer in the garden, had the wisdom to remain silent when falsely accused and to answer truthfully but cryptically as necessary, Peter, having failed to keep watch with Jesus, was having a much more difficult time. For immediately upon arriving with John, who was known to the high priest and to be a follower of Jesus by the door maid, he was caught off-guard by her question if he too was a follower of Jesus. No doubt unnerved by the events that had just transpired in the garden, including his wounding of the high priest’s slave for which he could easily have been charged with attempted murder, his immediate response was to deny it, supposing it to be a harmless deceit to a person of little importance. But there are no people of little importance from an eternal, spiritual perspective, however small their station in life. And because he was with John who was known by her to be a disciple, and it was the middle of the night, and Jesus had earlier been arrested and brought there, and Peter’s own accent gave him away as being from Galilee where Jesus was known to be from (Mat 21:11, 26:73), she couldn’t help but wonder if he was telling the truth. So rather than not drawing attention to himself, her suspicions were raised concerning him. Because Jesus’ arrest would have been a hot topic of conversation that night among the workers, she no doubt shared her suspicions with others, and was perhaps even the servant-girl who pointed out his connection to Jesus to those warming themselves with Peter around the fire. Unfortunately because of the very nature of truth, the more vehemently Peter denied it, the more suspicious he became, to the point that many were piling on him with the certainty that “surely you are one of them” (Mar 14:70; cf. Joh 18:26), and Peter, caught in a snare of his own making, could only double down with cursing and swearing in his denial.
What does Matthew record happened at that very instant? See Mat 26:74. How immediately does Luke say it happened that the cock crowed? See Luk 22:60. What time frame does Luke also give for when this last denial happened in relation to the first two? See Luk 22:58-59. What additional detail does Mark—who is believed to have obtained his information first-hand from Peter—give? See Mar 14:72. Consider Jesus’ earlier prediction that despite his bluster to the contrary Peter would deny Him three times before a rooster crowed twice (Mar 14:30), and the rooster had already crowed once at some point, probably just a short time before the second sounding due to the dawning of the day, but after his earlier denials. Although it is possible because of the stress of the evening that his denials simply didn’t register with him at the first sounding of the cock, is it also conceivable that the thought did at least to some degree cross Peter’s mind, but he either dismissed or suppressed it, perhaps because it was too painful to consider, and / or because he justified to himself that the circumstances gave him no other options? How is that like us when we are confronted by our sins, perhaps by some subtle pricking of our conscience from the Lord?
Is it also possible that Peter even resolved after the first sounding to not deny Him again, only to be confronted by the circumstances surrounding his third denial and the hole he had already dug for himself with his previous denials? Again, how is that like us when we are desirous of serving the Lord and resolve to not deny Him by our deeds (cf. Tit 1:16), but are not yet completely surrendered in our hearts to make a complete sacrifice and follow Him even unto death? Even at that time, instead of a third denial, how might a humble confession of his own failure and unworthiness with a bold declaration of Jesus’ goodness and innocence as demonstrated by His actions just earlier in the garden have been a powerful witness of the nature of true salvation to those in the high priest’s own household? How might keeping watch and praying with Jesus earlier that evening have fit Peter to do so? Although we may have health and wealth and strength and even a sword according to the world’s understanding for obtaining a successful outcome, what does Peter’s example earlier that night in the garden, in contrast with Jesus’, remind us was lacking, and why, that prevented him from following through on his desire to not deny Jesus but make a stand for Him? See Zec 4:6, Mat 26:37-38,40-41.
 Most versions of Mar 14:68 indicate that there was a first crowing between Peter’s first and second denials, but the reference is lacking in many early manuscripts. Thus it isn’t clear if it was inserted by later copyists as a point of reference for the second crowing in Mar 14:72.