Charles Ellicott Commentary Exodus 4:13

"And he said, Oh, Lord, send, I pray thee, by the hand of him whom thou wilt send." — Exodus 4:13 (ASV)

Send, I pray thee, by the hand of him whom thou wilt send.—Rather, please send by whom you will. A curt, impatient, and scarcely reverent speech. Moses means that he will undertake the task if God insists; but that God would do far better to send another. Hence the anger of the Lord against him (Exodus 4:14), which led to Aaron’s association with him as joint leader of the people.