It was because of the death of Waraqah ibn Nawfal, a Christian ascetic and close friend who believed in his prophethood. It was also a Christian monk named Bahira that announced his prophethood as a child.

The Prophet Muhammad (PBUH) loved Christians very dearly and his death drove him to profound despair. I can relate, the genocide of Muslims and Christians by zionist Jews has driven me to the point of suicide attempts before I embraced Islam, speaking anonymously.