All perfect praise be to Allaah, the Lord of the worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad, sallallaahu ‘alayhi wa sallam, is His slave and messenger.
Allaah has prepared Paradise as the dwelling place of the pious that have done good in this present life, and out of His Wisdom, He Created Paradise in ranks whereby its dwellers differ in status according to their deeds. Logically, this is absolutely fair, because a person who works hard must be rewarded differently from he who works little: they are not equal.
When the Prophet, sallallaahu ‘alayhi wa sallam, asked Rabee‘ah ibn Ka‘b Al-’Aslami to ask for anything he wanted, Rabee‘ah said he wanted to be with the Prophet, sallallaahu ‘alayhi wa sallam, in Paradise. In reply, the Prophet, sallallaahu ‘alayhi wa sallam, told him to perform the prayer and prostrate much in order to attain this rank. [Abu Daawood and An-Nasaa‘i]
This narration shows that much prostration is a means of reaching highest ranks in Paradise. Hence, you should know that the difference of degrees in Paradise is due to the difference of deeds from one person to another.
Islam means total submission to Allaah sticking to His Commandments and refraining from His Prohibitions. Besides, you should know that Allaah The Exalted does what He wills. Allaah Says (what means): {He is not questioned about what He does, but they will be questioned.}[Quran 21:23]
Thus, you should never ask why Allaah did this or that, rather you must fully submit yourself to Him, as He does not do anything without wisdom.
Finally, you should that Allaah is The Most Just and He does not wrong anyone. Allaah Says (what means): {And your Lord does injustice to no one.}[Quran 18:49] This is because of His Complete Justice.
Allaah Knows best.