Quran

Starting the verse with: (Indeed, your Lord knows that you [O Prophet] stand up), implies a praise for the Prophet (ﷺ) for carrying out what he was enjoined by Allah, Who cares for him and says: (Half of it, or a little less ` Or add to it), but the Prophet (ﷺ) chose the higher limit, which was nearly two-thirds of the night, as the Messengers of Firm Resolve would. Ibn Ashur: 29/280.
Question: The verse starts with: (Indeed, your Lord knows that you [O Prophet] stand up). Why?

Allah mentions their excuses, saying: (He knows that there are some among you who will be ill) so they cannot pray at night; (and others traveling in the land, seeking the bounty of Allah), which means that they travel for business and profits, and seek what they need from the grace of Allah for their livelihood, so they cannot pray at night; (and others fighting in Allah's way), the mujahideen, so they cannot pray at night. Allah mentions three reasons for waiving the obligation of nighttime prayer, and for these reasons, He waived it for the rest of Muslim Ummah. Al-Shawkani: 5/322.
Question: This verse mentions excuses for waiving the obligation of nighttime prayer. What are they?

The statement: (All-Forgiving, Most-Merciful) serves as a basis for seeking forgiveness, which means: Seek forgiveness because Allah is abundantly Forgiving and intensely Merciful. The aim behind this rationale is encouragement and inducement to seek forgiveness, as it will hopefully be answered. The mention of these two of Allah's Names that are in emphasized form is an indication of a promise of answer. Ibn Ashur: 29/290.
Question: The verse is concluded by, (for indeed Allah is All-Forgiving, Most-Merciful). Why?

Or it may be that what is meant by garments is garments in the usual sense, and that he was commanded to purify them and remove all impurities from them, at all times, especially when beginning to pray. As he was enjoined to purify himself outwardly, then outward purification is part of inward purification. Al-Saadi: 895.
Question: The command to purify the garments indicates inward purification. How?

(And purify your garments), Muhammad bin Sirin said: Wash them with water. Ibn Zaid said: The polytheists were not used to purifying [anything], hence, Allah commanded His Prophet (ﷺ) to purify himself and his garments. Al-Tabari: 23/12.
Question: What is meant by: (And purify your garments)?

Al-Zamakhshari said: (Not easy) could have been sufficed by (a difficult day), but this is to indicate that this difficulty will not be eased similar to what occurs in worldly life, which is a further warning to the disbelievers, and good tidings to the believers because it will be easy for them. Perhaps the two meanings are independent of each other, and (a difficult day) is a distinct description of that day and an illustration of its immense terror. Al-Shanqiti: 8/363.
Question: How are these two terms relevant to each other: (difficult), (not easy)?

They are not absent, which means that they are present with him. They do not travel for business trading. Rather, their servants and hired workers handle all of that for them while they are sitting with their father. He enjoys their company and delights in being with them. This was a great blessing in their living with him. Ibn Kathir: 4/442.
Question: What is the blessing of having one's sons present with him?