Imam Ibn Al-Qayyim (rahimahullah) said: “All of the Qur’an is regarding Tawheed. This is because the Qur’an is either:
1. Information regarding Allaah (the Most High), His names, His attributes, His actions and His statements. This is Tawheed in knowledge and information [regarding Him]. 2. A call to worship Him alone, He has not partners; and abandoning anything which is worshipped besides Him. This is Tawheed of one’s intent and seeking.
3. A command or a prohibition, and [an order to] maintain His obedience in His commands and prohibitions. This is from the rights of the Tawheed and its perfection.
4. Information regarding the honouring the people of Tawheed, and what happened to them in the Worldly life and what they will be honoured with in the Hereafter. This is the reward of Tawheed.
5. Information regarding the people of Shirk, and what happened to them in the Worldly Life from punishments; and what will happen to them in the final abode of punishment. This is the recompense of those who leave the command of Tawheed.
So the Qur’an, all of it, is regarding Tawheed, its rights and rewards, as well as regarding the state of Shirk, its people and their recompense.”
[Madaarij as-Saalikeen 3:417/418]