Allah has not made Faith universally accepted

Allah, the Exalted, informs that He is able to make all of mankind one nation upon belief, or disbelief. This is just as He said,

وَلَوْ شَآءَ رَبُّكَ لآمَنَ مَن فِى الاٌّرْضِ كُلُّهُمْ جَمِيعًا

Difference: Blameworthy and Praiseworthy

When it was said in the fifth verse (118) - ` had your Lord willed, He would have made all the people a single community' - the sense is that had it been the will of Allah, He would have made all human beings accept Islam by force. All of them would have then become nothing but Muslims without any difference remaining between them. But, such are the dictates of His wisdom that, in this world, Allah Ta` ala does not compel anyone to do something. Instead, He has entrusted man with a kind of choice under which he could do whatever good or bad he wishes to do. Then, human temperaments differ, ways differ and deeds differ. The outcome is that there always will be some people who would keep at loggerheads against the true faith - of course, with the exception of those whom Allah Ta` ala has blessed with His mercy, that is, those who have been following the noble prophets.