وَلَقَدْ أَنذَرَهُم بَطْشَتَنَاThus do We reward him who gives thanks. And he indeed had warned them of Our punishment,meaning, before the torment struck his people, he warned them of Allah's torment and punishment. They did not heed the warning, nor listen to Lut,فَتَمَارَوْا بِالنُّذُرِbut they doubted the warnings!i.e. but instead doubted and disputed the warning