First of all, let us not leave without attention the address the Lord uses here: "My friends." Not slaves, not servants, not even disciples, but friends. Who are friends? For us, they are those whom we love, with whom we do not want to part, and to whom we wish the very best. Now let us read what Jesus says to His friends as He warns them about future disasters, persecutions, and murders.
We would probably look for ways to avoid the coming danger and speak about reasonable caution... Jesus' words are unexpected: "Do not be afraid." Will the troubles pass by? No. But one must not fear death, physical death, because the murderer can do nothing more to us, and physical death is not yet the end. So if there is anything to take seriously, it is what separates us from the One who gives eternal life: sin. To take it seriously means trying to avoid it already here and now. For after death resurrection awaits us, and after it, judgment, which is carried out by the Judge who gave His life for our salvation. And if we are not filled with reverent trembling, which is called the fear of God in biblical language, before this Judge, then our path with Him is interrupted in Gehenna.