(12) I will be with thy mouth.--To suggest words (see Matthew 10:19-20), and assist utterance. Comp. the reluctance of Jeremiah (Jeremiah 1:6), and God's dealings with him (Jeremiah 1:7-9).

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.Now therefore go, and I will be with thy mouth,.... And put words into it, and cause it to speak readily and powerfully; and so it appears that he was mighty in words, as well as in deeds, Acts 7:22,

and teach thee what thou shalt say; to Pharaoh, to the Israelites, and to Aaron, that was to speak for him, as is hereafter observed.