“And Peter went out and wept bitterly.” — Luke 22:62.
"The word “carnal” comes from the Latin word for flesh. In Romans viii., and in Gal. v., we are taught that the flesh and the Spirit of God are the two opposing powers by which we are dominated or ruled, and we are taught that a true believer may allow himself to be ruled by the flesh." -Andrew Murray
Look at [Peter]...in the carnal state. What are the marks of the carnal state in him? Self-will, self-pleasing, self-confidence. Just remember, when Christ said to the disciples at Caesarea Philippi, “The Son of Man must be crucified,” Peter said to Him, “Lord, that can never be!” And Christ had to say to him, “Get thee behind Me, Satan!” Dear reader, what an awful thing for Peter! He could not understand what a suffering Christ was. And Peter was so self-willed and self-confident that he dared to contradict and to rebuke Christ! Just think of it! Then, you remember, how Peter and the other disciples, were more than once quarreling as to who was to be the chief—self-exaltation, self-pleasing;—every one wanted the chief seat in the Kingdom of God. Then again, remember the last night, when Christ warned Peter that Satan had desired to sift him and that he would deny Him; and Peter said twice over, “Lord, if they all deny Thee, I am ready to go to prison and to death.” What self-confidence! He was sure that his heart was right. He loved Jesus, but he trusted himself. “I will never deny my Lord”! Don’t you see the whole of that life of Peter is carnal confidence in himself. In his carnal pride, in his carnal unlovingness, in the carnal liberty he took in contradicting Jesus, it was all just the life of the flesh. Peter loved Jesus. God had by the Holy Spirit, taught him. Christ had said, “Flesh and blood hath not revealed this unto thee, but My Father which is in heaven.” God had taught him that Christ was the Son of God; but with all that, Peter was just under the power of the flesh; and that is why Christ said at Gethsemane, “The spirit is willing but the flesh is weak.”—“You are under the power of the flesh, you cannot watch with Me.” Dear reader, what did it all lead to? The flesh led not only to the sins I have mentioned, but last of all to the saddest of things, to Peter’s actual denial of Jesus. Three times over he told the lie; and once with an oath, “I know not the man.” He denied his blessed Lord. That is what it comes to with the life of the flesh. -Andrew Murray, The Deeper Christian Life
You may wish to read Self Absorbed?