To understand the Quran, you have to read it with an empty mind. Many verses of the Quran can help you in this. For example, there is a verse: الَّذِي خَلَقَ الْمَوْتَ وَالْحَيَاةَ لِيَبْلُوَكُمْ أَيُّكُمْ أَحْسَنُ عَمَلً (67:2)

From this and other verses, I understand that the main subject of the Quran is the creation plan of God. That is, to inform people about God's creation plan. This is the subject of the Quran. If you take a copy of the Quran and open it, in every page there will be mention of the Hereafter, Day of Judgment and fear of God. This will be mentioned in every page.

What does this mean? God's greatest concern is for a person to know that only a small portion of his lifespan is in the pre-death period. The bigger portion is in the post-death period. Here we live only a small part of our lifespan: 30, 40 or 50 years. After this, we enter the eternal period of life. This is the greatest concern of the Quran. A person should know before death that he has to face an eternal reality. Every person should know this before entering life after death.

A scholar has said that the Quran is a book of warning and glad tidings. The Quran is a book of inzar and tabshir. Inzar means to give warning and tabshir means to give glad tidings. You will see that the Quran warns about Hell and gives awareness about Hell.  And it also gives glad tidings of Paradise. Time and again the Quran tells you that there is life after death. There are Hell and Paradise in that world. Hell is meant for punishment and Paradise is for reward.

This is the subject of the Quran: to inform people about the plan according to which God has made this world and settled humans on earth. In the beginning, the Quran says: الْحَمْدُ لِلَّهِ رَبِّ الْعَالَمِينَ الرَّحْمَنِ الرَّحِيمِ مَالِكِ يَوْمِ الدِّينِ الْحَمْدُ لِلَّهِ رَبِّ الْعَالَمِينَ (1:2-4) God is Lord of the Day of Judgment. In the first sentence you read that God is Lord of the Day of Judgment. That is, we have to appear before Him one day.  A Day of Judgment is soon going to come. The subject of the Quran is to convey the creation plan of God.