If you read Llull's Ars Brevis, which is the best way to get familiar with his philosophy and theology and thus his manner of evangelizing Jews and Muslims, you find a fascinating section in Part X, Section 12, called The Hundred Forms, where he basically lays out certain definitions and relations so that the rest of his epistemological system can function correctly.
Llull is fascinating because he does not start, like Descartes, with doubting everything, nor does he start with just reason, but he starts with a moral universe and a real God, but not, ab initio, with a Christian God. The beginning point for his philosophy, or really his 'art', is virtue and the glory of God. This is how he can use his art to reason with Muslims and Jews and even Monophysites.
While he does not claim that his art proves from reason alone the Trinity, he does claim that it proves the Trinity is reasonable--a key flaw he saw in his days among others who were evangelizing Muslims.
His first step is to build common ground. Anyway, here are some sections from the Hundred Forms:
2. Essence is the form abstracted from and sustained in being.
12. Form is the essence with which the agent acts in matter.
50. Monstrosity is the deviation of natural motion.
64. Grace is a primary form, placed in the person receiving it without any merit on his part.
80. Theology is the science that speaks of God.
81. Philosophy is the subject by means of which the intellect concentrates on all the sciences.
