Jamieson, Fausset and Brown on 1 Samuel 22:5

5. the prophet Gad said unto David, Abide not in the hold--This sound advice, no doubt, came from a higher source than Gad's own sagacity. It was right to appear publicly among the people of his own tribe, as one conscious of innocence and trusting in God; and it was expedient that, on the death of Saul, his friends might be encouraged to support his interest.

forest of Hareth--southwest of Jerusalem.