In listing the three greatest understanders of Christianity in my personal judgment, it should be clear that what is being judged here is me, not the vast numbers of theologians who have vastly greater insight than myself but who I have not read, or not understood.
Anyway here they are.
1. St John the Apostle and Evangelist; author of the fourth Gospel, letters and Book of Revelation. Who knew Christ, was the first to understand and recognize Christ and his ministry, the disciple whom Jesus loved - and one of the most intelligent people in the history of the world.
2. St Paul the Apostle - Aristotle to St John's Plato; a different but equal intelligence; who met the resurrected Christ and was divinely inspired.
3. Blaise Pascal. The wonder of the modern world, a gift for us. Like John and Paul he completely understood the problem of the world and the human condition; and understood that only Christ offered an answer: that there is no other answer, not even in theory.