10. The sentence, “My breast straitens”, shows that Prophet Moses (peace be upon him) was somewhat hesitant of going alone on such a difficult mission, and also had the feeling that he was not eloquent in speech. That is why he begged Allah to appoint Aaron too, as messenger to assist him who, being more vigorous in speech, could support and strengthen him as and when the need arose. It is just possible that in the beginning, the Prophet Moses (peace be upon him) might have begged that Aaron be appointed to Prophethood instead of him, but later when he felt that Allah willed him to be appointed to that position, he might have appealed that Aaron should at least be made his counselor and assistant. We say this because here Prophet Moses (peace be upon him) is not praying for Aaron to be made his counselor, but says: Appoint Aaron to Prophethood. On the other hand, in Surah Ta Ha, he says: Appoint for me a counselor from my family, (let it be) my brother Aaron. Then in Surah Al-Qasas, he says: My brother Aaron is more vigorous in speech than myself, so send him as an assistant with me to confirm (and support) me. From this it appears that these two requests were made later, but originally Prophet Moses (peace be upon him) had begged Allah to appoint Aaron to Prophethood instead of himself.
The Bible has a different story to tell. According to it, Prophet Moses, fearing that he would be rejected by the people of Pharaoh, and putting forward the excuse of his faltering speech, had declined to accept his appointment to prophethood on the pretext that he lacked vigor and eloquence in speech: O my, Lord, send, I pray Thee, by the hand of him whom thou wilt send. (Exodus, 4: 13), Then Allah, of His own will, appointed Aaron to be his assistant and persuaded them: to go together before Pharaoh. (Exodus, 4: 1-13). For further details, see (E.N. 19 of Ta Ha).