That is my favorite ikon by Rublev. It is believed there was a mirror on the table so that when a person looked at the icon they would see their face and recognize they are invited to the table. The scene of the Holy Trinity as depicted in the icon comes from the Book of Genesis: “The LORD appeared to Abraham near the great trees of Mamre while he was sitting at the entrance to his tent in the heat of the day. 2 Abraham looked up and saw Three men standing nearby. When he saw them, he hurried from the entrance of his tent to meet them and bowed low to the ground. 3 He said, “If I have found favor in your eyes, my Lord, do not pass your servant by. 4 Let a little water be brought, and then you may all wash your feet and rest under this tree. 5 Let me get you something to eat, so you can be refreshed and then go on your way—now that you have come to your servant.” “Very well,” they answered, “do as you say.” 6So Abraham hurried into the tent to Sarah. “Quick,” he said, “get three seahs of the finest flour and knead it and bake some bread.” 7 Then he ran to the herd and selected a choice, tender calf and gave it to a servant, who hurried to prepare it. 8He then brought some curds and milk and the calf that had been prepared, and set these before them. While they ate, he stood near them under a tree. 9 “Where is your wife Sarah?” they asked him. “There, in the tent,” he said. 10 Then one of them said, “I will surely return to you about this time next year, and Sarah your wife will have a son.” Now Sarah was listening at the entrance to the tent, which was behind him.” (Genesis 18:1-10, Holy Bible, NIV)