(Act according to your ability,) This means, "Act according to your current ways." This is actually a severe threat.
(I am acting.) according to my way.
(You will come to know who it is on whom descends the torment that will cover him with ignominy, and who is a liar!) meaning, between me and you.
(And watch you!) This means to wait.
(I too am watching with you.) Allah then says,
(And when Our commandment came, We saved Shu`ayb and those who believed with him by a mercy from Us. And As-Sayhah (awful cry) seized the wrongdoers, and they lay (Jathimin) in their homes.) His saying Jathimin means extinct and lifeless without any movement. Here Allah mentions that a loud cry (Sayhah) came to them. In Surat Al-A`raf He says a severe quake (Rajfah) came to them. In Surat Ash-Shu`ara', He said it was a torment of a cloudy day. They were one nation upon which all of these punishments were gathered on the day of their destruction. In each context, Allah only mentioned that which was suitable. In Surat Al-A`raf when they said,
(We shall certainly drive you out, O Shu`ayb, and those who have believed with you from our town.)7:88 In this verse it was suitable to mention a tremor, or quake (Rajfah). The earth in which they practiced their wrongdoing and they wanted to expel their Prophet from it, shook them. Here, due to their disrespectful manners in speaking to their Prophet, Allah mentioned the awful cry (Sayhah) which overcame them and killed them. In Surat Ash-Shu`ara' when they said,
(So cause a piece of the heaven to fall on us, if you are of the truthful!)26:187 Allah said in response,
(So the torment of the day of Shadow seized them. Indeed that was the torment of a Great Day.)26:189 This is from the intricate secrets and to Allah belongs all praise and much bounty forever. Concerning the statement,
(As if they had never lived there!) This means it was as if they had not lived in their homes before that.
(So away with Madyan as just as Thamud went away!) They (Thamud) were their neighbors and they did not live far from the homes of the people of Madyan. They were similar in their disbelief and their highway robbery. They were also both Arabs.