The Holy Patriarch Abraham and his wife Sarah, in receiving three strangers with ardent hospitality, actually served with their small means and great hearts the Holy Trinity, Who appeared to them in the form of Three Angels before the Oak at Mamre, now in present day Hebron, Israel. This is the first appearance of the Triune God together in visible form that is recorded in the Holy Scriptures. God draws close to all who call upon Him in grace, truth, and love, even though we are weak and limited in our understanding, although not seen usually in such an outwardly visible form, or such a lively perceptible interaction to our humanity.
Here in this modern Greek icon, the Holy Trinity is seen as They appeared in the form of the Three Angels, and are shown symbolically sitting down before a table to partake of what Abraham and Sarah are shown bringing to Them. It is right after such service that the Lord God promises to Abraham and Sarah that they will have a natural son, Isaac, who will be the fulfillment by God of the former promise and everlasting covenant of God with men and with his seed forever after him. We are in that promise.