If you were to look for an icon of the Holy Trinity, surprisingly the most famous one takes its inspiration from the Old Testament, from today's first reading (Gn. 18). In this reading Abraham gives us the perfect model of Hospitality.
When we think of virtues we think of things like patience, or the three theological virtues of faith, hope and love. In the OT one of the most important virtues is that of hospitality. As a somewhat nomadic culture, they understood that it was necessary for survival. We understand it as an aspect of love.
In the story three men are coming down the road. They do not approach Abraham and ask for help. It is Abraham, as the good host, who goes out and invites them, begs them, to do him the favor of stopping. He then goes on to offer them the best that he has.
After they have eaten they tell him that this time next year he will have a son. And we get the famous moment when Sarah laughes.
Later Christian iconographers, like Andrei Rublev, will use these three men as the image of the Holy Trinity.
It is worth noting that at the time Abraham offered the hospitality to the strangers, he had no idea that they were any thing more than travelers. Abraham saw three men traveling on a hot road and felt compassion. His compassion gave rise to his hospitality.
Most of us would like to think that we are compassionate. The real measure, it would seem, is whether or not our compassion moves us to action. If not, are we truly compassionate, or is our compassion merely an abstract idea in our minds?
Like all virtues, the only way we grow in them is by practice.