Habib `Umar b. Hafiz (may Allah preserve him) said,
This is why the poet said
و مزدريهم لو كان مسكا … لقيل في أصله نجاسة
Whoever respects people will be respected by them, and will win unto intelligence and leadership.
But someone who has contempt for them, were he to be made of musk, he would be told that he was originally filth. 
This is why we must approach people with love, concern, mercy, and compassion. And that is how the Prophet (Allah bless him and give him peace) came to you: he was all mercy, compassion, humility, and politeness. This is why you will find that most of the early ones to respond to his call were the downtrodden people of Mecca … At the conquest of Mecca, Bilal  was the only one who climbed the Ka`ba when the Prophet (Allah bless him and give him peace) told him, “Climb and call the people to prayer.” (Habib `Umar b. Hafiz, Tawjih al-Nabih li Mardati Barih, Kuwait: Dar al-Diya, 2008, p. 167)
 Musk comes from the originally filthy secretions of the musk-deer that collect in a sac and solidify.
 In other words, at the height of the Prophet’s political supremacy (Allah bless him and give him peace).
 A former slave.