The Hand of Musa turning White without any Disease

This is the second sign of Musa. That is Allah has commanded him to place his hand into the opening of his garment, as is clearly stated in another Ayah. It mentioned here merely as a passing reference, saying:

وَاضْمُمْ يَدَكَ إِلَى جَنَاحِكَ

Good companions are a help in the better performance of worship and Dhikr (remembrance)

كَيْ نُسَبِّحَكَ كَثِيرً‌ا وَنَذْكُرَ‌كَ كَثِيرً‌ا (So that we proclaim Your purity a lot and remember You a lot - 20:33, 34). The advantage of making Sayyidna Harun a Wazir and a partner in prophethood would be that both of them together would be able to pray to Allah Ta` ala and glorify His name more often. Here the question may arise that a man by himself can also pray as often as he desires, so where was the need for a companion? The answer to this is that good companions and a conducive environment definitely contribute towards the better performance of worship and Dhikr. A person whose friends are negligent about Allah cannot devote himself to His worship with the same quality and quantity as the person who is fortunate to have the company of pious men and righteous friends devoted to Allah's worship and Dhikr.