"They have not appraised Allah with true appraisal," meaning: they have not venerated Him with His true veneration, by worshipping idols instead of Him which, if the fly steals from them...
﴿مَا قَدَرُوا اللَّهَ حَقَّ قَدْرِهِ﴾ أَيْ: مَا عَظَّمُوهُ حَقَّ عَظَمَتِهِ؛ بِأَنْ عَبَدُوا الْأَوْثَانَ مِنْ دُونِهِ الَّتِي إِنْ سَلَبَهَا