﴿ وَمَاذَا عَلَيْهِمْ لَوْ ءَامَنُوا۟ بِٱللَّهِ وَٱلْيَوْمِ ٱلْءَاخِرِ وَأَنفَقُوا۟ مِمَّا رَزَقَهُمُ ٱللَّهُ ۚ وَكَانَ ٱللَّهُ بِهِمْ عَلِيمًا ﴾

“And what would they have to fear if they would but believe in God and the Last Day, and spend [in His way] out of what God has granted them as sustenance - since God has indeed full knowledge of them?”

And what burden is on them if they were to believe in God and the Last Day and expend of what God has provided them? that is to say what harm would this cause them? In other words there is no harm therein. Rather harm lies in what they follow the interrogative is meant as a disavowal; the law of law āmanū ‘if they were to believe’ conveys the sense of the verbal noun sc. mādhā ‘alayhim īmānuhum ‘what burden would their belief be upon them?’. God is ever Aware of them and will requite them for what they have done.