Saint Thomas Aquinas held that there are certain realities that can be discovered and known through reason alone (such as the existence of God), while we depend on the revelation of God for our knowledge of others (such as the Incarnation.) However, I believe there is a third category. I believe there are some things that cannot be arrived at directly through reason alone, but once presented to the intellect through revelation, can be known by reason as being necessarily true.
I was reflecting on this idea, specifically in regards to the trinitarian nature of God, when a Trent Horn podcast came on, during which he conversed with a Sam Tideman, a "biblical unitarian." During the first part of the podcast, Trent and Tideman discussed various biblical texts in regards to unitarianism. There are three things I took away from listening to the discussion. The first is the realization that unitarianism isn't what I thought it was. The second is frustration that the biblical texts that Trent brought up didn't include a couple I thought he should talk about. The third is that, now that trinitarianism has been given to us, especially in the Scholastic model, there's really no way, intellectually and philosophically, to hold a unitarian view of God.
My first encounter with the idea of unitarianism was through my wife. She is a convert to the Church, but before I met her, she had bounced around between various Protestant sects. At one time, she briefly joined up with some unitarians in college. From her telling of it, they only always pray (and do anything else) in the name of Jesus, because "Jesus" is the name of the Father and of the Son and of the Holy Spirit. Although she didn't know the word (and neither did I at the time,) her understanding of unitarianism was basically modalism.