An-Nisāʾ: 131
"And to Allah belongs whatever is in..."
"From before you"
It is connected to waṣṣaynā (We have enjoined) or ūtū (those who were given).
"And you"
It is a conjunction linked to alladhīna ūtū (those who were given).
"The Scripture"
A generic noun encompassing all heavenly books.
"That you fear [Allah]"
Meaning: bi-an tattaqū (that you should fear). An is explanatory because the injunction carries the meaning of a command.
"And if you disbelieve, then to Allah..."
It is a conjunction linked to ittaqū (fear). The meaning is: "We commanded them and We commanded you to have taqwā (piety), and We said to them and to you: If you disbelieve, then to Allah [belongs all that is in the heavens and the earth]." The meaning is that to Allah belongs all of creation; He is their Creator, their Owner, and the Bestower of all types of blessings upon them. Therefore, His right is to be obeyed in His creation and not disobeyed.
"They fear His punishment and hope for His reward."
"And We have enjoined upon those who were given the Scripture before you and [upon] you that you fear Allah"
This means it is an ancient injunction that Allah has always commanded His servants. You are not singled out by it, for through taqwā they attain happiness with Him, and through it, they attain salvation in the end. We said to them and to you: "And if you disbelieve, then to Allah belongs whatever is in the heavens and the earth," from among the angels and the two heavy groups (jinn and mankind) who profess His oneness, worship Him, and fear Him.
"And Allah is ever..."
Despite all that...
"Free of need"
Independent of His creation and all their worship. He is worthy of being praised for the abundance of His blessings, even if none of them praise Him.
"To Allah belongs whatever is in the heavens and whatever is in the earth"
This is a confirmation of the reason for His taqwā, so that they may fear Him, obey Him, and not disobey Him, for fear and piety are the root of all good.
"If He wills, He can do away with you"
He can annihilate you and cause you to cease to exist, just as He brought you into existence and created you.
"And bring others"
He can create other people in your place, or other creations besides mankind.
"And Allah is ever over that..."
Of annihilation and creation...
"Competent"
Possessing supreme power; nothing He wills is impossible for Him. This is an expression of anger toward them, a warning, and a demonstration of His omnipotence. It is also said that this is an address to those among the Arabs who were hostile to the Messenger of Allah (ﷺ), meaning: "If He wills, He can cause you to die and bring other people who will support him."
"And it is narrated that when this was revealed, the Messenger of Allah (ﷺ) struck the back of Salman with his hand and said: 'They are the people of this man.'"
(Transmitted by al-Tabari from the hadith of Abu Hurayrah; in its chain is Abd al-Aziz ibn Muhammad al-Darawardi, who is truthful.) He means the people of Persia.