Masaccio. The Holy Trinity with the Virgin, St. John and Two Donors. - Olga's Gallery

If you do art history, knowledge of Catholicism is a must. Popes and pious patrons during the Renaissance especially spent enormous amounts of money on art, and the artists involved tried to merge classical learning with Christian thought and make sense of the whole jumble.

Here, in Masaccio's "The Holy Trinity," take note of the Roman archway and the hall it frames. That creates the idea that the Father is moving towards us, the dove (the Holy Spirit) is moving down upon us, and we, of course, facing the painting are drawn towards them. The meeting point, of course, is Christ on the cross.