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I.e., that God is not enough to succour him: obviously an allusion to the type of man who "worships God on the border-line of faith" (verse {11} above) and therefore doubts His power to guide men towards happiness in this world and in the hereafter. The assumption of the majority of the commentators that the personal pronoun "him" relates to the Prophet Muhammad is, to my mind, very far-fetched and certainly not warranted by the context.
The rendering of la-yaqta' as "let him [try to] make headway" is based on the accepted, tropical use of the verb qata'a (lit., "he cut") in the sense of "traversing a distance": and this is the interpretation of yaqtac by Abu Muslim (as quoted by Razi). The expression "by any [other] means" (bi-sabab) relates to what has been said in verses {12-13} above.
Lit., "that which causes anger" or "exasperation", i.e., anguish at finding himself helpless and abandoned.
Meaning, no matter what the deniers do, Allah will never stop supporting His Prophet (ﷺ).
There is some difference of opinion as to the interpretation of this verse. Most Commentators are agreed that the pronoun "him" in the second line ("will not help him") refers to the holy Prophet, and that the "any" in the first line refers to his enemies, who wished to see him destroyed and removed from the scene of his labours. Ibn 'Abbas, whom I have followed here, and whom a great number of Commentators follow, construes the later clauses in the sense given in the text. Freely paraphrased, it means: if the enemies of Allah's Messenger are enraged at his successes, let them fix a rope to their ceiling and hang themselves. Samaa is thus rendered by the word "ceiling". If Samaa is rendered by the word "heaven" (the usual meaning), the paraphrase would be : if the enemies of Allah's Messenger are enraged at the help he gets from heavens, let them stretch a rope to heavens, and see if they can cut off the help in that way!-in other words, they are fools if they think they can intercept Allah's help by their petty devices!