You know that the Qur'an is absolutely Decisive. No Muslim can doubt its principles.
3:85 Whoever seeks as a Way of Life other than Islam, it will never be accepted from him, and in the life Hereafter, he will be among those who have completely lost their investment. [This is because the Deen (Religion) of the entire Universe is Submission]
Here is a sh'er of Allama Iqbal:
BA-MUSTAFA BERASAAN KHWAISH RA KEH DEEN HAMA OOST
AGAR BA-OO NARASEEDI TAMAAM BU-LAHABEEST