If Christianity is considered monotheistic, then why is there a holy trinity? What is the difference between the father, son, and the Holy Spirit? If God is to be considered as one, then why does he have all of these aspects?
Well, it is so because the Church fathers said it was so and in the third century after Christ if you said any different you were burned as a heretic and thousands were burned for saying this very thing. It takes some real philosophical gymnastics to come up with the Trinity. Islam and Judaism see Christians as polytheists and idolaters. Polytheists because of the Trinity and idolaters because Christians make “graven images” of God in contravention of the second commandment.
During the Reformation many breakaway Protestant sects actually raided Cathedrals and destroyed priceless stained glass art, ornate altars, paintings and religious icons because they were seen as blasphemous and pagan. These were the original iconoclasts
Imagine. People fought wars over this.