The Christian God (The Trinity) is composed of three elements: the Son, the Father, and the Holy Spirit.
I went to Catholic school all my life. I grew up learning about the Christian religion all throughout kindergarten to high school. I learned that they worship a man named Jesus (the Son) who lived on this earth and then ascended to Heaven. I also learned that almost all Christians believe in the Trinity and that it makes up one God. Later on, I was surprised to find out that Hinduism believes that their one God is composed of not three, but three hundred thirty million gods.
But why is that Hinduism is considered a polytheistic religion while Christianity is considered a monotheistic religion?
It's because Christianity has Bible verses that advocate monotheism, even though there are verses that contradict them to advocate the Trinity. It's because three forms of One God seems a lot less polytheistic than three hundred thirty million forms of One God. Polytheism in general is viewed as more primitive and has negative connotations to it which is why most Christians deny being polytheistic. Christians have a lot of cultural power to influence society, so society tends to not think of them as polytheists. Society associates Christianity with monotheistic religions such as Judaism and Islam.
However, Jews and Muslims don't believe that their one God is composed of any elements. Judaism and Islam are strictly monotheistic. They strictly believe in the oneness of their God without it being composed of separate forms. Jews and Muslims are strictly against worshipping a person who lives/lived on this earth. They don't believe that their one God has a son.
No ladies and gentlemen, Christians do not worship the same God as the Jews and Muslims. So therefore, Christianity should not be grouped with Judaism and Islam in a picture like this...
This picture pretty much sums up how society lies about Christianity and monotheism. Along with Hinduism, it's best to describe Christianity as soft polytheism, which is the belief in one God who has three or more different forms.