he will be a wild man - literally, “a wild ass man,” expressing how the wildness of Ishmael and his descendants resembles that of the wild ass.
his hand will be against every man - descriptive of the rude, turbulent, and plundering character of the Arabs.
dwell in the presence of all his brethren - dwell, that is, pitch tents; and the meaning is that they maintain their independence in spite of all attempts to extirpate or subdue them.