Overall meaning : Allah commands His Prophet, Muhammad, may Allah bless him and grant him peace, to ask the Jews and Christians, by way of reproof, what has induced them to deny the proofs Allah mentions in their books, which confirm his prophethood and the truthfulness of his message, and to let them know that Allah is fully aware of all their actions and nothing is hidden from Him.
He also instructs him to ask them, by way of reproof, why they endeavour to mislead and turn the believers away from the path of Allah, seeking to make it appear crooked when they themselves know the truth and are aware of their evil deeds. Allah is not unaware of what they do.