Quran

This is a promise and an assurance from Allah. If one asks: how can something which is a favor from Him becomes (upon Allah)? The answer is that any promise made by Allah becomes a reality since He never breaks His promise. Ibn Juzay: 1/391.
Question: How can something which is a favor from Allah becomes (upon Allah)?

Allah did not say, "Which of you has done the most deeds." Rather, He says, (best in deeds). A deed cannot be considered a good deed until it is done sincerely for Allah, the Mighty and Sublime, and it must be in accordance with the Sunnah of Allah's Messenger (ﷺ). Whenever a deed lacks one of these conditions, then it is null and void. Ibn Kathir: 2/419.
Question: What is the difference between "most deeds", and (best in deeds)? Why is the latter term used?

The best deed is attained by two things, first: It is done sincerely for Allah, seeking thereby the Countenance of Allah, and not associating partners with Him. Second: It is ordained by Allah, loved by Him, conformed to the rules of Sharia, and not invented. Fudhail bin Iyadh said about this verse (which of you is best in deed): "The deed that is done sincerely and correctly." Ibn Taimyah: 3/507.
Question: How does a deed become (best)?

Man is just as described by Allah; when he faces hardship after prosperity, he becomes despaired of having an end to the hardship in the future, and is ungrateful for the prosperity he had before. When he gains prosperity after hardship, he feels secure from ever facing hardship again in the future, and forgets what he has been through by saying: ("All my ills are gone," and becomes exultant and boastful). Ibn Taimyah: 3/508.
Question: Explain the state of man when he is tried by prosperity and by hardship.

One of the indications of patience is expecting relief. The term (who are patient) is used instead of "who believe" to give the opposite meaning to the state of disbelievers mentioned in the previous verse, (he becomes utterly despaired and ungrateful). Ibn Ashur: 12/15.
Question: The verse uses the term (who are patient) instead of "who believe." Why?

These verses indicate that it is inappropriate for someone who calls people to Allah to be deterred by the objections and criticisms of people; especially if this criticism is baseless and does not undermine the message to which he is calling them. Al-Saadi: 378.
Question: In this verse, there is a lesson to those who call others to Allah. What is it?

The breadth of mind of the Prophet (ﷺ) is indicated in this verse by the use of a variation of the adjective (distressed) in the original Arabic text. Ibn Juzay: 1/392.
Question: How does this verse indicate the breadth of mind of the Prophet (ﷺ)?