al-Shūrā 42:31

Wa mā antum bi-muʿjizīna fi'l-arḍ; wa mā lakum min dūni'llāhi min waliyyin wa lā naṣīr

"You cannot thwart Him on the earth. And you have, apart from God, neither protector nor helper."

ʿAjz, in the root's original sense, is to be left behind in a matter, to fail to keep up. ʿAjuz — the hind part of a thing, the rear. The lexicographers make the link thus: the one who cannot do a thing is left behind it.

Muʿjiz (an active participle of Form IV) — "one who renders another powerless". The sentence, that is, does not say "you are not powerless"; it says "you cannot render Him powerless".

And the redundant bi- reinforces the negation — as with bi-wakīl in the sixth verse.

The second half of the sentence is the sentence of the eighth verse. I set the two side by side:

The same sentence, with two different persons, twenty-three verses apart. This is a fact that can be verified from the text and was recorded in the section on the structure of the sūra.

I record this as my own reading: a verdict spoken in the third person is about someone standing at a distance; spoken in the second person it comes upon the reader. The sūra gives the same verdict twice, from two different distances.

And the qualification min dūni'llāh has been added: in the eighth verse this qualification was not there. The sentence, that is, leaves an exception here: there is none apart from God — God Himself stands outside this.