[2:211] Ask the Children of Israel how many a clear proof did We give them; whoever changes God's grace after it has come to him, God is severe in retribution.
The benefit of questioning was to make them acknowledge the question of proof. Questioning them was not for the purposes of resolving any doubt on the part of the Messenger (ṣ) concerning what had been plainly established by proof.
Whoever changes God's grace after it has come to him, God is severe in retribution in taking this grace away. At that moment they will recognize its worth and will then mourn it as they will never attain it. The one who spoke for them said:
You will leave
and abandon me.
You will seek
but not find me.