declare what is to be reported about God—that He is the One, the Ever-Sufficient—and in this sūrah He says:

Say, O disbelievers, I do not worship what you worship.
(109:1–2)

Thus He ordered him to announce that he worships none of what they worship besides Allah, for he worships none but Allah alone.

The same meaning appears in His words:

So to that, invite and stand firm as you have been commanded; do not follow their caprices. Say: I believe in whatever Book Allah has sent down, and I have been commanded to deal justly between you. Allah is our Lord and your Lord. Our deeds are ours and your deeds are yours; there is no argument between us and you.
(al-Shūrā 42:15)

That is, there is no dispute. The term ḥujjah (argument) refers to whatever a litigant adduces, even when it is false; it is not a condition of the word ḥujjah that it be true. When it is true, it is called a bayyinah, a burhān, or a dalīl. Hence the Exalted said:

so that mankind would have no argument against Allah after the messengers
(al-Nisāʾ 4:165)

and:

so that people may have no argument against you, except those of them who have done wrong.
(al-Baqarah 2:150)

Those wrongdoers are the polytheists, who advance a spurious plea against you, saying, “He has returned to our qiblah; soon he will return to our religion.” This is how the verse was explained by the Companions and the Followers who excelled after them. Some later commentators, however, claimed that illā here carries the sense of “and,” construing the verse to mean, “so that people may have no argument against you, and those who did wrong among them…”—but their reading is shown to be unsound from many angles.