# come on him

This means to purposefully go to where he is and then to attack.

# we will cover him as the dew falls on the ground

"we will overwhelm and completely defeat David's army"

# dew

the fog or misty cloud of water that can fall onto the ground during the night, covering the ground and leaving it wet in the morning

# We will not leave even one of his men ... alive

"We will kill every one of his men"

# him himself

"David himself"