Such, then, is a spurious argument advanced by the wrongdoers.

What further clarifies the matter is His later statement:
“Those who dispute about Allah after He has already been acknowledged—their argument is void in their Lord’s sight; upon them rests wrath, and for them is a severe punishment.” ⦗Ash-Shura 16⦘

Thus He still calls it an “argument” yet declares it void. Those who dispute about Allah after He has been acknowledged are the unbelievers, whether pagan idol-worshippers or People of the Scripture. They contend with the believers in order to make them abandon their religion.

Concerning the Christians He said:
“If anyone disputes with you about him after knowledge has come to you, then say, ‘Come, let us call our sons and your sons, our women and your women, ourselves and yourselves; then let us pray earnestly and invoke Allah’s curse upon the liars.’” ⦗Āl ʿImrān 61⦘

In this way the disbelievers argued with the believers to turn them back from their faith, even as they harmed them. Such people have a void argument before their Lord; upon them is wrath, and for them is a severe punishment.

Their disputation with the believers amounts to sheer wrongdoing, aggression, and the propagation of falsehood. Therefore the Exalted One commanded him to say:
“There is no argument between us and you.” ⦗Ash-Shura 15⦘

Meaning: you have no right to wrong us or to assault us with your hollow argument.