[M]any Christians have denied Jesus when faced with persecution. The most obvious example of this is Peter—he denied Jesus three times, yet Jesus directly told him that he was still a follower of Christ (John 21:19). So on the one hand, the heart of the gospel is a truth worth dying for (as evidenced by Jesus and most of the Apostles), but on the other hand the gospel offers forgiveness even to those who deny Christ.
This is potentially confusing because of 2 Timothy 2:12: “If we endure, we will also reign with Him; If we deny Him, He also will deny us.”
But the denial in this verse is not talking about the momentary denial like Peter, or like a student scared for his life in the face of a gunman. That denial references the absolute walking away from the faith; apostasy. And in that case, there is no salvation.
This verse seems so drastic, and that is the point. Paul—himself facing martyrdom (4:6)—challenges his readers to persevere. But Paul does not want true believers to lose heart, and so he immediately follows verse 12 with: “If we are faithless, He remains faithful, for He cannot deny Himself” (2 Timothy 2:13).
There will always be moments where we lose faith, but for those who are in Christ, we should have confidence that while we may lose faith, Jesus may never lose us. Even if we momentarily are gripped by fear, and value our lives more than the life of Christ, Jesus still possesses us, and he cannot deny himself.
Even so, Johnson says, you should say you are a Christian if an answer is demanded of you, even at the risk of death. He explains why you need not worry about whether or not you would be strong enough to do this in the rest of his article.