Some scholars interpret the exceptive sentence 'except that which Allah wills' differently. They say that for some reason Allah blots out temporarily a verse from Holy Prophet's memory, but he may remember it again, in support of which the following narrative may be adduced: One day the Holy Prophet (SM) recited a Surah, but omitted one of the verses. Sayyidna Ubayy Ibn Ka'b رضي الله عنه, one of the Prophet's (SM) scribes, was present. He thought it might have been abrogated. On inquiry, the Holy Prophet (SM) said that it was not abrogated, but that it was omitted by mistake. [Qurtubi]. In this interpretation, it may be summarised that forgetting a verse temporarily, and then remembering it again, does not go against the promise made in this verse. [In fact, it is an exception from this promise.] Allah knows best!
وَنُيَسِّرُكَ لِلْيُسْرَىٰ (And We will facilitate for you [to reach] the easiest way....87:8).The phrase 'the easiest way' refers to the sacred laws of Islam. Apparently, according to the demand of the context, it should have been stated 'We will make the Shari'ah easy for you'. But the Qur'an chose, instead, to state 'And We will facilitate for you (toreach) the easiest way. . The reason for that, probably, is to indicate that Allah will predispose him to the sacred laws, so that they will become part of his nature, and he will become an embodiment of Shari'ah.
فَذَكِّرْ إِن نَّفَعَتِ الذِّكْرَىٰ (So, extend advice [to people] if advice is useful....87:9) The preceding verses described the facilities created by Allah for the Holy Prophet (SM) in performing his Prophetic obligation. This verse commands him to perform his obligation. The verse contains the conditional particle 'in' (if) that apparently makes the sentence a conditional statement. But, in fact, the command is not intended to be made conditional. It is rather an emphatic statement.This is similar to the grammatical phenomenon in many languages. The particle 'if' is sometimes used when something is always true. It is used for introducing a situation that always has the same meaning, result or effect. For example: "If you are a 'man' [obviously he is a man], then you will have to do this work;" In neither of such sentences, the particle 'if is conditional, but rather emphatic. Likewise, the verse purports to say that preaching truth and righteousness is certainly useful. Therefore, the beneficial thing should never be abandoned at anytime.
قَدْ أَفْلَحَ مَن تَزَكَّىٰ (Success is surely achieved by him who purifies himself,..87:14)The word tazakka is derived from zakah, the primitive meaning of which is 'to purify'. The zakah of wealth is so called because it purifies the rest of man's wealth for him. In this context, the word tazakka is used in a general sense, which comprehends the purity of faith and character, and purity of wealth.
وَذَكَرَ اسْمَ رَبِّهِ فَصَلَّىٰ (and pronounces the name of his Lord, then offers prayer....87:15). This covers all categories of prayer, obligatory as well as supererogatory. Some commentators say that it refers especially to 'Id prayers. This interpretation too can fall under the preceding category.