Why did Allah create 7 heavens? I am aware that only Allah knows the answer, but is it explained in the Quran why there are 7 heavens?
Imagine that there are two people X and Y. Let's say that X prays more than 5 times a day, fasts a lot more than average, and basically worships God better than most other people. Now, let's say that Y tries to pray five times a day (but misses some of them), does not fast everyday in Ramadan, and worships God less than X. Do you think it would be fair if God gave them both the same reward? Do you think God should ignore all the efforts that X has shown in order to be closer to God?
So yes of course heaven has different levels depending on your actions in this life and how much you strive to be closer to God. However, it is a promise from God that nobody will be upset in heaven. So people from lower levels will never feel jealousy for those that are above them. Everybody will be happy but in different levels. Also, this doesn't mean that these people from different levels will be separate from each other.
The following is from a tafsir called the Risale i Nur about the hadith "Everyone will be together with those he loves" (Bukhàri, Àdâb, 96; Muslim, Birr, 165; Tirmidhi, Zuhd, 50; Da'wât, 98)
QUESTION: According to the meaning of:
Everyone will be together with those he loves,4
in Paradise, friend will be together with friend. Therefore, love for God's sake kindled in a simple nomad during one minute's conversation with the Prophet (PBUH), means he has to be with the Prophet (Peace and blessings be upon him) in Paradise. But since God's Noble Messenger (PBUH) receives limitless effulgence, how can it be united with that of a simple nomad?
THE ANSWER: We shall allude to this elevated truth with a comparison. For example, a magnificent personage set up a vast banquet and finely-adorned spectacle in a splendid garden. He prepared it in such a way that it included all the delicious foods that the sense of taste can experience, and all the fine things that please the sense of sight, and all the wonders that amuse the faculty of imagination, and so on; he included in it everything that would gratify and give pleasure to the external and inner senses. Now, there were two friends and they went together to the banquet and sat down at a table in a pavilion. But the sense of taste of one of them was very limited, so he received only minor pleasure. His eyes could see only a little, he had no sense of smell, and he could not understand the wondrous arts nor comprehend the marvels. He could only benefit from and take pleasure in a thousandth or even a millionth of that beautiful place, to the extent of his capacity. The other man however had developed his outer and inner senses, his mind, heart, emotions, and subtle faculties so perfectly and to such a degree that although he was next to his friend, he could perceive and experience all the subtleties and beauties and marvels and fine things in the exhibition, and receive their different pleasures.
Since this confused, sorrowful, and narrow world is thus, and although the greatest and the least are together, the difference between them is as great as from the ground to the Pleiades, surely in Paradise, the realm of bliss and eternity, while friend is together with friend, each will receive his share from the table of the Most Merciful and Compassionate One in accordance with his capacity and to the extent of his abilities. Even if the Paradises in which they are found are different, it will not be an obstacle to their being together. For although the eight levels of Paradise are one above the other, the roof of all of them is the Sublime Throne.5 If there are walled circles round a conical mountain, one within the other and one above the other from its foot to the summit, the circles are one over the other and look to one another, but do not prevent each other seeing the sun. There are also various narrations of Hadiths indicating that the Paradises are in a manner close to this.
In the text of Quran it’s mentioned that hell has 7 doors:
"And indeed, Hell is the promised place for them all. It has seven gates; for every gate is of them a portion designated."15:43,44(Surat Al-Ĥijr,verse 43 and 44)
But there isn't any verse in Quran to mention number of heaven doors. Although, it mentions which heaven has different doors:
"But those who feared their Lord will be driven to Paradise in groups until, when they reach it while its gates have been opened and its keepers say, "Peace be upon you; you have become pure; so enter it to abide eternally therein," [they will enter].39:73( Surat Az-Zumar,verse 73)
In different hadiths, it has mentioned that heaven has 8 doors.
Imam Muhammad al-Baqir(a.s.):"heaven has 8 doors."
That doors are created for different people with different acts, means, and good people will go to heaven from a door which is related to their act. They will pass a door which is related to the best and the most important act of them; one door for fasting persons, one for soldiers of the holy war, one for thankful persons of god and etc...
But heaven has different levels, too. People goes to different levels according to their merit.
Prophet in interpretation of surat Ar-Rahman said: جنتان من ذهب للمقربین و جنتان من ورق لاصحاب البمین There are 2 golden paradisiacal garden for favourite of Allah and 2 silver paradisiacal garden for ashabe yamin. Which shows heaven has different levels.
Levels of heaven are as many as levels of people who goes to heaven. And their level in heaven is related to their acts.
Usually it is said levels of paradise are equal to the number of verses in Quran and by knowing and practicing a verse in life one goes to higher level. In fact who knows, obeys and practices all verses of the Quran during his life will reach the highest level of paradise. Only reading or memorizing Quran is not enough, although memorizing them has it's benefits.
No, there are 7 skies, not 7 heavens. There is one and only one heaven.
However doors are 7 of 1 heaven. But there is no context where it is stated that Allah created 7 heavens.
7 doors are because of different tests on people, such as, prayers, fasts, behaviour toward other people etc. People would pass through each segment and would enter the Heaven. But the heaven is just one!
However, I have read about the Stages in Heaven, the top most stage for prophets and so on, but I have never heard that there are other Heavens then the one we know.