In the second verse (89), Sayyidna Shu'aib (علیہ السلام) said to his people:Allah Ta` ala saved us from your false faith. Now if we were to return to your faith, this would amount to a false and grim accusation by us against Allah Ta` ala.
First of all giving Kufr and Shirk the status of faith by itself means that they have been commanded by Allah Ta` ala - which is forging a lie against Him. In addition to that, after having believed in the revealed Truth ('Iman) and after having its knowledge and insight, a return to Kufr (disbelief) would amount to saying that the first way was false and erroneous while the true and correct way was that which has been adopted later. As obvious, this is a compounded lie and accusation - that the true (Haqq) was taken to be false (Bath) and vice versa, the Bath to be Haqq.
There was a certain flavour of claim or assertion in this saying of Sayyidna Shu'aib (علیہ السلام) - that we can never return to your religion again. Making such a claim is, at least outwardly, contrary to the spirit of selfless submission a true servant of Allah is supposed to have ('abdiyyah). It does not behove those who are close to the presence of Allah and those who have come to know Him. Therefore, he said: مَا يَكُونُ لَنَا أَن نَّعُودَ فِيهَا إِلَّا أَن يَشَاءَ اللَّـهُ رَبُّنَا ۚ وَسِعَ رَبُّنَا كُلَّ شَيْءٍ عِلْمًا ۚ عَلَى اللَّـهِ تَوَكَّلْنَا (And it is not for us that we turn to it unless Allah, our Lord, so wills. Our Lord encompasses everything with His knowledge. In Allah we place our trust).
This statement is a mirror of his humility عِجز ('Ijz), an assertion of trust in Allah تَوَکُّل (Tawakkul) and a confident attitude of resigning matters to Him تفویض (Tafwid). These are master virtues of prophets. They amount to saying: at are we and how can we claim to do something or stay away from it? To be able to do something good and to succeed in staying away from evil is nothing but the grace of Allah Ta'ala – as said by the Holy Prophet ﷺ :لَو لَا اللہُ مَا اھتَدَینا وَ لَا تَصَدَّقنَا وَ لَا صَلَّینَاHad there not been the grace of Allah Ta'ala, we would have not been guided right, nor been able to give in charity, nor to make Sarah.
It was due to this quality of trusting in Allah alone that when, after having talked to the arrogant chiefs of the people, Sayyidna Shu'aib (علیہ السلام) realized that nothing seems to move these people in any manner whatsoever, he stopped addressing them and made the following Du'a' (prayer) to Allah Ta'ala: رَبَّنَا افْتَحْ بَيْنَنَا وَبَيْنَ قَوْمِنَا بِالْحَقِّ وَأَنتَ خَيْرُ الْفَاتِحِين (Our Lord, decide between us and our people, with truth, and You are the best of all judges). Sayyidna 'Abdullah ibn 'Abbas ؓ has hat the word: فَتح (fath) means 'decide' at this place. That is how the word: فَاتِح (fatih) takes the sense of Qadi or judge.
And in reality, through these words, Sayyidna Shu'aib (علیہ السلام) had prayed for the destruction of the disbelievers from among his people - which was answered by Allah Ta'ala when they were destroyed by an earthquake.
