The High Priestly Prayer
In the church I was born in it was never taught about being born again, and that would include not one single word about the Trinity.
This meant that the Holy Spirit was ignored, and forgiveness not mentioned. When one of us kids asked why Jesus had to die on the Cross, no one in the Sunday School had a ready answer.
In the church I was married in, the pastor, an intellectual sort who authored books, likely read mostly by other intellectuals, was dismissed by a faction in the congregation who just did not like him.The reason many Protestant churches are a certain size is that it is at a certain size they will split, around 500 in my experience.
I only realized how important the Trinty was when a person came to the door and explained to me just how important the Trinty actually was. That was what I thought, not whatever precisely what he thought. That was when John 17, began to lead me to the workings of the Trinity.