Do not be afraid of those who kill the body but cannot kill the soul. Rather, be afraid of the one who can destroy both soul and body in hell.
Jesus is instructing his disciples on what to preach and giving them advice before they went out to spread the gospel in Israel. In this verse, there is another verbal affirmation by Jesus that hell exists.
We should not be afraid of people that will do physical harm to us. As our body is a vessel for our souls. If our body dies our soul is alive in the spirit. But rather we should be afraid of the one (satan) who will destroy our body and soul forever in eternity in hell. We should really think about what Jesus is saying here. He is giving us a direct message on the correct spiritual path to follow in our life. We should make every effort in our lives to walk beside God, have a relationship with God and have faith so that he will grant us entry into heaven.