Virtually no other mystery of God alludes our grasp so much as the revelation of the Trinity. It does not permit a visual presentation.  Therefore, in the church symbols like the equilateral triangle and the circle are usually used to represent this mystery.  The Trinity has also been visualized as the "Throne of Grace".

The Eastern Church uses only one biblical account as the prophetic symbol of these mysteries: Abraham's banquet in the forest of Mamre where he offered hospitality to three unknown guests who prophecy the birth of Isaac.  The alternation between "we" and "I" in the speech of the
 guests was one of the grounds that led the early church to see in this text the first distinguishable symbolic revelation of the Triune God.

- The basis for the representation is found in the biblical story of Genesis 18:1-15.  Word and   picture are intimately connected in icons...
- The artist Rublev reduced the extensive story to the essentials...
- Within this picture Rublev sought to represent the moment in the conversation between the   Divine figures when the decision was made to send the Son in human form to accomplish   the work of redemption.  (Lasarew interprets, convincingly for me, the left figure as the   Father, the middle figure as the Son, and the right figure as the Holy Spirit.)
- In the middle of the picture stands the chalice of the Eucharistic meal through which comes   the decision of God to pardon humankind including ourself (the form of the chalice appears   more times in the icon).  .
- The closed orifice on the front side of the table is the place in the altar where the relics of the   martyrs are kept.  The Eucharist unites us with those already justified...

- Andrei Rublev - The Trinity  (Meditation on picture)
Let the message which the artist wants to bring through the icon embrace you and permeate you more and more...