For he supposed his brethren would have understood him,
 &c.] From his being an Hebrew in such high life; from his wonderful birth, and miraculous preservation in his infancy, and education in Pharaoh's court; and from the promise of God that he would visit them and save them: 
 how that God by his hand would deliver them:
 wherefore he was the more emboldened to kill the Egyptian, believing that his brethren would make no advantage of it against him; but look upon it as a beginning and pledge of their deliverance by him: 
 but they understood not;
 or "him not", as the Ethiopic version reads; they did not understand that he was to be their deliverer, or that this action of his was a token of it.