The following is extracted from The Jewels of the Qur’an by Imam Abu Hamid al-Ghazali (r.a.).
The secret of the Qur’an, its purest pith, and its ultimate aim consist in calling people to God, the Most Powerful, the Lord of this World and the Hereafter, the Creator of the heavens above and the layers of earth below, and whatever is between them and whatever is under the moist subsoil. For this reason the suwar of the Qur’an and its verses are limited to six types of which three are precedents and important principles and three follow them, enrich them and complete them.
As to the three important divisions, they concern the definition of God to Whom men are called, the definition of the straight path, perseverance in which is required in advancing towards Him, and the definition of the condition at the time of attaining to Him.
As to the three divisions which enrich them and complete them, one describes the conditions of those who answer to the Call to God, and His Delicate Dealings with them, the secret and the purpose of this being to excite a desire and to encourage them. It also describes the conditions of those who shrink from answering to the Call and the manners of the Suppression and Punishment of them by God, the secret and the purpose of this being to provoke consideration and fear.
The second division narrates the conditions of those who deny God, and reveals their disgrace and their ignorance in disputing and arguing against the Truth. The secret and the purpose of all this being, on the side of falsity, to make manifest and to create aversion, and, on the side of truth, clear apprehension, confirmation and constraint.
The third division defines the stages of the path to God and the manner of taking provision and preparation for it.