Moses wanted to see if someone would step forward, and, impelled by zeal for the cause of God and for God's law, would declare himself ready to avenge the outrage. He waited in vain. Then he determined to act himself. Naturally enough he hesitated to take the life of a human being.
He did not know whether the evil-doer might not be brought to repentance, and then lead a life of pious endeavor. He also considered, that there would perhaps be some among the descendants to spring from the Egyptian for whose sake their wicked ancestor might rightfully lay claim to clemency. The holy spirit allayed all his doubts. He was made to see that not the slightest hope existed that good would come either from the malefactor himself or from any of his offspring.
Then Moses was willing to requite him for his evil deeds. Nevertheless he first consulted the angels, to hear what they had to say, and they agreed that the Egyptian deserved death, and Moses acted according to their opinion.