Charles Ellicott Commentary Exodus 4:12

"Now therefore go, and I will be with thy mouth, and teach thee what thou shalt speak." — Exodus 4:12 (ASV)

(12) I will be with thy mouth. —To suggest words , and assist utterance. Compare the reluctance of Jeremiah (Jeremiah 1:6), and God’s dealings with him (Jeremiah 1:7–9).