Islam is very clear in the fact that only those who believed in God in the pure monotheistic manner as described in the Holy Quran will enter Paradise. If one was to think of Paradise having a door and every door having a unique key. Then, the unique key to the door of Paradise is pure monotheism.
So, a person must believe in one true god and worship him in the manner that befits him and he must treat all of God’s creation with maximum respect and honor. It is insufficient to be ‘good’ to creation whilst being ‘bad’ to God by denying his very existence.