Why did Peter deny Jesus three time's even after he said he would follow Jesus to the death? The simple answer is that he wasn't ready in his heart and mind to face death for Jesus and likely for anyone else either!
It takes years of preparation, deliverance, maturity, and spiritual growth to be able to stand before an angry mob, religious leaders, or even government officials and say I love Jesus, I believe in the scriptures of the bible, and I stand for the truth contained therein.
I was recently pondering, and said to my wife I wonder what the outcome would have been if Peter would have said, "Yes! I know Jesus, He's my best friend, I love Him, and He loves me!" Likely he wouldn't have been martyred because God had big plans in store for Peter, we know that today, but he didn't know that then!
In the same way, how about the rich young ruler? He had a hard decision to make too, didn't he?
Matthew 19:16-22
"Now behold, one came and said to Him, “Good Teacher, what good thing shall I do that I may have eternal life?” So He said to him, “Why do you call Me good? No one is good but One, that is, God. But if you want to enter into life, keep the commandments.” He said to Him, “Which ones?” Jesus said, “‘You shall not murder,’ ‘You shall not commit adultery,’ ‘You shall not steal,’ ‘You shall not bear false witness,’ ‘Honor your father and your mother,’ and, ‘You shall love your neighbor as yourself.’ ” The young man said to Him, “All these things I have kept from my youth. What do I still lack?” Jesus said to him, “If you want to be perfect, go, sell what you have and give to the poor, and you will have treasure in heaven; and come, follow Me.” But when the young man heard that saying, he went away sorrowful, for he had great possessions."Even though Jesus said, it's hard for a rich man to enter the kingdom of God, I wonder how much the rich young ruler would have been blessed if he would have done what Jesus said! It may have been hard for him to obey, but not impossible!!!
The original twelve disciple Jesus called during the beginning of His ministry all had hard decisions to make.
Matthew 4:18-22
And Jesus, walking by the Sea of Galilee, saw two brothers, Simon called Peter, and Andrew his brother, casting a net into the sea; for they were fishermen. Then He said to them, “Follow Me, and I will make you fishers of men.” They immediately left their nets and followed Him. Going on from there, He saw two other brothers, James the son of Zebedee, and John his brother, in the boat with Zebedee their father, mending their nets. He called them, and immediately they left the boat and their father, and followed Him."These disciples left their jobs, their homes, their family members, their spouses, and their old lifestyles behind to follow Jesus!
And likewise in the near future, every person on earth will have have to make a decision that will determine where their immortal soul resides for all eternity.
Revelation 13:15-17
"He was granted power to give breath to the image of the beast, that the image of the beast should both speak and cause as many as would not worship the image of the beast to be killed. He causes all, both small and great, rich and poor, free and slave, to receive a mark on their right hand or on their foreheads, and that no one may buy or sell except one who has the mark or the name of the beast, or the number of his name."