The LORD is my light and my salvation; whom shall I fear?
The LORD is the strength of my life; of whom shall I be afraid?
When the wicked, even mine enemies and my foes,
 came upon me to eat up my flesh, they stumbled and fell.
Though an host should encamp against me, my heart shall not fear:
though war should rise against me, in this will I be confident.

David is telling us here that he has nothing to fear because he has placed his trust in the Lord and so why should he fear men?  His enemies cannot hurt him in any real sense because he is immortal in spirit.