And three of the thirty - The word שלשים shalishim, which we translate thirty, probably signifies an office or particular description of men. Of these shalishim we have here thirty-seven, and it can scarcely be said with propriety that we have thirty-seven out of thirty; and besides, in the parallel place, 1 Chronicles 11:11-47, there are sixteen added. The captains over Pharaoh's chariots are termed שלשים shalishim, Exo 14:7.
The Philistines pitched in the valley of Rephaim - This is the same war which is spoken of Sa2 5:17, etc.

And three of the thirty chiefs went down,.... Or three that were chief of the thirty, superior to them; which some understand of the three before mentioned, so Josephus (w); and that having related some particular exploits of theirs, here observes one, in which they were all concerned; and others think the three next are meant, of whom Abishai was the chief, Benaiah the next, and the third Asahel; but the first sense is best:

and came to David in the harvest time, unto the cave of Adullam; not when he was there, upon his flight from Saul, Sa1 22:1; but after he was king, when engaged in war with the Philistines; perhaps wheat harvest is here meant:

and the troop of the Philistines pitched in the valley of Rephaim; the army of the Philistines, as the Targum; of the valley of Rephaim; see Gill on Jos 15:8.

(w) Antiqu. l. 7. c. 12. sect. 4.