Aye, THERE'S the rub, Ann Archy. You've expressed the difference: simply lying to a murderer is not "turning your back on Jesus." And I believe if we dug deeper into the scripture quoted, we'd find that that was Jesus' intent in this message: live your life as my follower.
To have eternal life you must accept Jesus as your Savior. So does knowingly lying to a murderer about your faith mean YOU haven't accepted Jesus as your Lord and Savior? I hardly think so.
Over there in the hot sands of the peninsula, that means being a follower of Jesus. Hence, if he denies it, he denies being a follower of Jesus, meaning he denies that Jesus is who He said He was.
This isn't difficult.
Tell you what. Come Judgment Day, why don't you approach God's throne with this kind of logic and see how far you get with it?
Its a LOT more than this. It means going to your death, if that is what you are called upon to do. Revelations speaks of being obediant UNTIL DEATH, then and only then will Christ grant the "crown of life"..to those who DO his will. You "Faith-Only-and-Nuthin-Else" types really have a lot to learn about the concept of obedience. Jesus prefers DOers as opposed to SAYers.