Allah did not send a prophet except that he tended sheep

All prophets tended sheep sometime during their life, and the apparent meaning of the Hadīth indicates that this was before their being prophets. Scholars said that the wisdom behind this (i.e. herding sheep) is for a person to be trained to look after people and direct them to what is good for them; because a shepherd sometimes directs the flock to the pasture, and sometimes keeps them standing still, and other times takes them back to the pasture.

The Prophet (may Allah's peace and blessings be upon him) was being prepared for taking care of the Ummah and directing it to all what is good, based upon knowledge, guidance and insight; just as the shepherd who has knowledge of the best pastures, and sincerely directs the sheep to wherever there is good, nourishment and water for them.

Sheep were chosen in particular because the one who tends sheep possesses the traits of tranquility, calmness and serenity, unlike the ones who tend camels, and who are mostly harsh and tough, because camels are harsh and tough too. That is why Allah, Glorified and Exalted, chose for His messengers to be shepherds to be trained and accustomed to taking care of people.