Perhaps you still do not understand what I mean. Reading the entire Bible is not, by itself, a sufficient basis for knowing the truth. The Bible scholars who hold the four different views concerning the identity of the Lord Jesus did not merely read the Bible from beginning to end; they also studied it for five to ten years. Therefore, each of their beliefs concerning the identity of Jesus is based on something they believe is written in the Bible, and they did not simply invent their beliefs, as you seem to think about the Trinity.
Why is it that you have already read the entire Bible, yet you have not studied the different understandings that these scholars have concerning the identity of Jesus? If you say that Arianism is not found in the Bible, and if we also include the Jehovah's Witnesses' doctrine and the Oneness doctrine, they would say the same thing to you, that the Trinity you believe in is not found in the Bible either.
Can you show them the actual word “Trinity” in the Bible that you believe in?