Tafsir of Al-Hashr 59:4

(That) — meaning what has descended upon them and what will descend — (is because they opposed Allah and His Messenger) and committed the abominable deeds they committed. (And whoever opposes Allah) — Talha read it as yushaqiq (with the unjoining of the letter), as in [Surah] al-Anfal. The restriction to mentioning opposition to Him, Exalted is He, is because it implies opposition to His Messenger, peace and blessings be upon him, and it contains an element of horror regarding the matter, and so that it corresponds to His saying, Exalted is He: (For indeed, Allah is severe in penalty).

This sentence is either the retribution itself, with the pronoun referring back to [the subject] omitted according to those who require it — meaning: He is severe in penalty toward him — or it is a justification for the omitted retribution, meaning: Allah will punish him, for Allah is severe in penalty. Whichever it may be, the conditional clause is a completion of what preceded it, an affirmation of its content, and a verification of the causality by way of demonstration. It is as if it were said: That which has descended and will descend upon them of punishment is because of their opposition to Allah, Exalted is He, and His Messenger, may Allah’s peace and blessings be upon him. And whoever opposes Allah, Exalted is He — whoever he may be — then because of that, there is for him a severe penalty; therefore, there is indeed a severe penalty for them.