Thomas Aquinas,
Summa Theologiae — Question 40 - OF CHRIST'S MANNER OF LIFE…
“ To know the Creator and the creature is the entire teaching of wisdom. The Creator is the Trinity, the Father, the Son, and the Holy Ghost. Now the creature is partly invisible, as the soul, to which the number three may be ascribed, for we are commanded to love God in three ways, 'with our whole heart, our whole soul, and our whole mind' ”
