It has caused a lot of division and strife.
It is part of why Muslims are hostile to Christianity and it is partially what led to the splitting of the Catholic Church.
The Bible doesn't mention it, but many people do.
It is the concept of the Trinity.
This post looks at the nature of the Trinity of the Christian God, and why it is complex.
A basic idea of the Trinity it that it represent the "Triune" God, consisting of God the Father, God the Son and God the Holy Spirit.
Three in One.
Confusing?
To put the concept in perspective, an ancient quote might help.
Theologian St. Augustine of Hippo went so far as to say the concept of the Trinity is "inaccessible to human reason". This idea stuck through the centuries.
However, its' mystery naturally leads to a question.
That question is, "how can God be three "persons"?One way this to be decided was a gathering of Clergy.
At the Council Of Nicea around 325 A.D., they discussed the nature of Jesus and his Divinity, to try and clear this question up. There were about 300 Bishops there, debating their opinions on the matter.
Discussing his Divinity was in addition to their other goal. That is, deciding if Jesus was eternal or created like any other human.
Heresies were rampant at the time regarding Jesus. (A heresy is a belief contrary to Orthodox Catholic doctrine).
Arianism was the biggest of these heresies, which asserted Jesus was a mortal human, and not the Son of God, This heresy was the core of what brought the Council together.
Other heresies were Docetism, Modalism and Socinianism, which looked as the Godhead as different "modes."
It was confusing how the parts of the Trinity worked together, and especially of how Jesus fit in.
In a nutshell, the Council essentially declared that Jesus was Divine and the Godhead was "one substance." (not three). They also concluded Jesus was an eternal being, and not created. The "one substance" was made of three equal parts.
That substance was made of three equal parts.
But some were still confused.
Some then concluded the Trinity actually meant there were three Gods, if Jesus was eternal.
How did this get "twisted"?
Islam's Prophet Muhammad thought Jesus was a son in a human sense, like being born from a mom and dad. Naturally, that would be confusing. This is despite the findings of the Council of Nicea.
Some Muslims infer that in Christianity there are three Gods, which is blasphemous.
However, it is important to note the concept of the Trinity does mean there are three Gods with three different wills.
(There can be three "persons", but not three Gods, even though each part is Divine).
One reason the idea might be inaccessible to reason is this; each part of the Trinity is distinct, yet where one is present they are all present.
Does that make sense?
For simplification sake, St. Augustine said to think of it this way;
Think of God as fire, and Jesus as the light from the fire. They have the same essence (nature), but are manifest in distinctly different ways.
This one substance was surprisingly capable of presenting itself all at the same time.
It was at the Baptism of Jesus (Theophany) God was present for the first time in all three forms. God the Father said "This is my Son, in whom I am well pleased." Jesus was the incarnate Son of God, and the Holy Spirit descended in the form of a dove.
It is important to note this does not represent three Gods. It represents God manifesting himself in three forms.
It is also important to note the idea of the Trinity is found from analyzing the Bible. Even though the word Trinity is not there, the concept is.
But - if you think about it - are you more than one representation as a person? You might be a son to one person, a father to another and a grandfather to another. Does that mean you are more than one person?
Like St. Augustine said, a person might never understand the concept of Trinity, since it is beyond a human's ability to comprehend.
Perhaps someday in heaven you will get to comprehend the idea. Until then, it is good to work with what you know.
What you can know is God chose three ways to show himself to you.