Complex sentence: Unitarians, like the early Pentecostals and those who take the bible literally, had to know the bible very well to argue what they consider the fallacies of the bible and support their trinity-less doctrine.
Split into simpler sentences: Unitarians, like the early Pentecostals and those that take the bible literally, had to be very adept to the bible. They knew the bible very well to argue the fallacies of the bible and support their trinity-less doctrine.