Apparently some substantial number of Muslims believe Christianity is polytheistic, based on the doctrine of the Trinity. I never felt the Trinity to be particularly important or relevant.
I thought the Trinity referred to three different manifestations of one God in much the same sense as one man can be a father, a son, an employee, a team member, and a neighbor. That said, I’m certain there are those who view it as vital, perhaps even essential to Christian belief.
Anyway, the article’s author, one Tarek Fatah, says the Trinity is a major issue for Muslims, a possible motive for slaughtering Christians. Who knew? Hat tip to Instapundit for the link.