4:10-17 Moses continued backward to the work God designed him for; there was much of cowardice, slothfulness, and unbelief in him. We must not judge of men by the readiness of their discourse. A great deal of wisdom and true worth may be with a slow tongue. God sometimes makes choice of those as his messengers, who have the least of the advantages of art or nature, that his grace in them may appear the more glorious. Christ's disciples were no orators, till the Holy Spirit made them such. God condescends to answer the excuse of Moses. Even self-diffidence, when it hinders us from duty, or clogs us in duty, is very displeasing to the Lord. But while we blame Moses for shrinking from this dangerous service, let us ask our own hearts if we are not neglecting duties more easy, and less perilous. The tongue of Aaron, with the head and heart of Moses, would make one completely fit for this errand. God promises, I will be with thy mouth, and with his mouth. Even Aaron, who could speak well, yet could not speak to purpose, unless God gave constant teaching and help; for without the constant aid of Divine grace, the best gifts will fail.
14. the anger of the Lord was kindled against Moses—The Divine Being is not subject to ebullitions of passion; but His displeasure was manifested by transferring the honor of the priesthood, which would otherwise have been bestowed on Moses, to Aaron, who was from this time destined to be the head of the house of Levi (1Ch 23:13). Marvellous had been His condescension and patience in dealing with Moses; and now every remaining scruple was removed by the unexpected and welcome intelligence that his brother Aaron was to be his colleague. God knew from the beginning what Moses would do, but He reserves this motive to the last as the strongest to rouse his languid heart, and Moses now fully and cordially complied with the call. If we are surprised at his backwardness amidst all the signs and promises that were given him, we must admire his candor and honesty in recording it.