# I have been with you

Here "with you" means that Yahweh has helped and blessed David.

# cut off all your enemies

Yahweh destroying David's enemies is spoken of as if Yahweh cut them off, as one would cut a piece of cloth or cut a branch from a tree.

# I will make you a name

"I will make your name to be great and well known" 

# the great ones

The phrase "great ones" means famous persons.