Allah, the Exalted, says, `We sent a Messenger to the people of Madyan.' They were a tribe of Arabs who lived between the land of the Al-Hijaz and Ash-Sham, close to the land of Ma`an. Their land was known by the name of their tribe and was thus, called Madyan. Allah sent unto them the Prophet Shu`ayb and he was of the noblest of them in lineage. For this reason, Allah said,
(their brother Shu`ayb.) Shu`ayb commanded them to worship Allah alone without associating any partners with him. He also prohibited them from cheating in their weights and measures (for business transactions).
(I see you in prosperity) meaning, `in your livelihood and your provisions. And verily, I fear that you will be deprived of this bounty that you are enjoying by violating Allah's prohibitions.'
(and verily, I fear for you the torment of a Day encompassing.) This means the abode of the Hereafter.