What is the Westminster Confession of Faith?
To determine if your beliefs are actually biblical, and that you are indeed a "Christian" i.e. believer in Christ, believer in the Bible without adding or subtracting anything, and follower of His Church, they came up with this in the 15th century. It is an excellent distillation of Biblical truth, and remains an excellent yard stick by which to measure your understanding of the Bible and your own faith. Coming up with your own theology, after it's been studied for more than a thousand years, is no better idea than inventing your own moral code. It simply has the worst possible track record of any idea man ever had. The WMCF certainly doesn't answer any mysteries or solve any disagreements about minutia among the sects of Christianity, but it does put forth those basic beliefs, that are very clear in the Bible, that all versions of the Christian faith have in common. There are and always have been non-Christian cults that use the Bible and the name of Jesus to justify their teaching, and the WMCF is a good place to start to identify them, because all of them mix apostacy with the truth to mislead you.
The Trinity is a doctrine, or a way of thinking about the Bible. The idea of Father, Son, and Holy Spirit is fraught with mystery. It's just a way of thinking about the concepts the bible puts forth as truth, while organizing them in a simple and easy way to understand, what we are not capable of understanding in this reality, that is "not wrong".
Short Version of the Catechism
It is very safe to say that if you don't agree with these central tenants you are not a "Christian". You may be something close to one, or approximating one, but you clearly don't understand or believe in the words written in the Bible. The Catholics believe stuff that I don't believe, but it is because they have chosen to consider some verse of the Bible literally rather than figuratively, and probably vice versa. On the big things "we" all agree. Were my understating to change slightly I could easily become a Catholic. As it is I'm very comfortable with the small amount of wisdom I've been graced with, and consider them my brothers in Christ, as they consider me. Same thing for almost every main line or evangelical church.
Sometimes people think The Bible is an engineering manual or a wiring diagram. To read it that way is to almost automatically misunderstand and misinterpret it. It's not an engineering manual. It is full of deeper meaning but written simply so any goat herder can understand the basics. I like to say that in the deeper mysteries, like explaining how a being can be in three places at once, or outside of time, the words the Bible uses are not wrong, but certainly don't try to explain it using quantum physics or string theory. These are mysteries, and intentionally so. Shallow enough so that you won't drown, and deep enough so that you can never find the bottom. It's a symphony, and you have to teach yourself to read music to understand it. We have to have faith that after this reality is over for us, and we're no longer confined to The Fourth Dimension, we will understand completely. The choice is to be in the presence of God, or to be separated from Him.
