Why do Christians not need to fear being killed by men?
Christians need not fear being killed by men because men can only touch the physical body, not the invisible, immortal part. That part will one day be resurrected. The resurrection of Christ changed the disciples from fear to boldness, and the same hope sustains believers, as Paul indicates.
Les teaches that back in the Gospels, one thing changed the total attitude of the eleven disciples, who at the crucifixion scattered and ran for their lives out of fear: the resurrection. After Christ rose from the dead, Peter never again would have kowtowed to a young maid and sworn he never knew Him. Peter stood up to Rome, and all eleven apostles, as near as can be told, were martyred without fear. Why? Because of the truth of resurrection. The same is true for us. We can say with Paul that we do not have to worry about what men can do to this body, because they cannot touch the invisible, immortal part of us, which will one day be resurrected if they kill us. This makes all the difference for a Christian. We have the hope of the power of resurrection, first in salvation, out of deadness, as Ephesians 2:1 says: You hath He quickened, made alive, who were dead in trespasses and sins. How did He do it? The power of resurrection. Then the text declares Christ to be the Son of God with power, according to the Spirit of holiness, by the resurrection from the dead, and through whom Paul received grace and apostleship for obedience to the faith among all nations for His name.