Jabir bin 'Abd Allah said that he was told by 'Umar bin Al Khattab that he heard the Apostle of Allaahﷺ say "I will certainly expel the Jews and the Christians from Arabia and I shall leave only Muslims in it".
The Prophet Muhammad's decision was based on his belief that Islam was the true religion and it should be followed by all people living in this region. He wanted to ensure peace and harmony among all people living in this area by having everyone follow one faith - Islam - which would bring about unity amongst them all. This hadith also serves as a reminder for us today to remain loyal to our faith no matter what obstacles come our way or how much opposition we face from those who do not share our beliefs or values.