God Smash!

The image of God which is presented to us in the 18th psalm is extremely warlike, a far cry from the loving and forgiving God that most of us learned about while growing up.   The odd thing about the imagery being used, however, is that it raises the implication that God is less powerful than the omnipotent omni-being much of the Bible presents him as.  The fact that he requires a cherub to ride upon or darkness to hide behind calls to mind the way people portrayed the "lesser" gods of polytheism, who were far closer to being human with the addition of some specific divine magic.  

This would make Psalm 18 ideal for appealing to people who would have a hard time dealing with the idea of a ubiquitous God capable of doing anything.   By seeming to lessen Him, the psalm actually casts Him in a more sympathetic light and allows Him to avoid Superman Syndrome (wherein a character is so powerful that it is impossible to form an emotional connection with them or care about their trials).  

It is far easier to imagine and emphasis a God who rides into battle with specific magics than it is to make a connection with a being who can solve problems by willing them to go away before they happen.