The Trinity, Part II - Profound Peace and Unity

Icon of the Old Testament Trinity, c. 1410, Andrei Rublev

... all three are wearing blue garments as a sign of the divine nature they have in common. But on top of or underneath the blue garments, each one has a distincitive color: the Father, the angel to the left, has an indefinable color almost of pure light as a sign of his invisibility and inaccessibility. The Son, in the center, is wearing a dark tunic as a sign of the humanity with which he has clothed himself. The Holy Spirit, the angel to the right, wears a green mantle as a sign of life, since he is "the one who gives life." ...

One thing is especially striking as we contemplate Rublev's icon: the profound peace and unity that emanate from the whole. A silent cry comes forth from the icon: "Be one as we are one." The saint for whose monastery the icon was painted, St. Sergius of Radonezh, is known in Russian history for having brought unity among warring chieftains and for having thus made possible the liberation of Russia from the Tartars, who had invaded it. His motto was that "through the contemplation of the most Holy Trinity we can overcome the hateful divisions of this world."

Contemplating the Trinity: The Path to Abundant Christian Life by Fr. Raniero Cantalamessa