It depicts a little boat floating on the waves, with the Greek word oikoumene overhead.
Their caption reads as follows:
The ecumene (US) or oecumene (UK; , oikouméne, “inhabited”) was an ancient Greek term for the known world, the inhabited world, or the habitable world. Under the Roman Empire, it came to refer to the civilized world and the secular and religious imperial administration. In present usage, it is used as the noun form of “ecumenical” and describes the Christian Church as a unified whole or the unified modern world civilization. It is also used in cartography to describe a type of world map (mappa mundi) used in late Antiquity and the Middle Ages.
What’s the deal with the boat?
There is an ancient tradition of using nautical themes to describe the Church. You might have heard the Church described as the “Barque of Peter” — barque being an old word for a ship. Peter, succeeded by the rest of the popes, pilots the boat.
The analogy is kind of cool — the Church, though buffeted by the tumult and turmoil of human existence, will alway stays afloat. It brings people together from across the world, and we can all jump aboard this big ocean liner on the way to Heaven. Note: there are no lifeboats. If things get bad, you have to go down with the ship. They don’t tell you that until you’re on board, though.
Let’s go deeper and take a look at Luke 5: 1–6:
While the crowd was pressing in on Jesus and listening to the word of God, he was standing by the Lake of Gennesaret. He saw two boats there alongside the lake; the fishermen had disembarked and were washing their nets. Getting into one of the boats, the one belonging to Simon, he asked him to put out a short distance from the shore. Then he sat down and taught the crowds from the boat. After he had finished speaking, he said to Simon, “Put out into deep water and lower your nets for a catch.” Simon said in reply, “Master, we have worked hard all night and have caught nothing, but at your command I will lower the nets. When they had done this, they caught a great number of fish and their nets were tearing.
Note that Christ does his teaching from Simon Peter’s ship. Coincidence? Probably not.
There are so, so many other analogies and parallels between the Church and boats, casting out nets, fishing, rough seas, etc., that it would be tedious to list them here.
In ecclesiastical architecture, the nave of a church is the long, rectangular part where the congregation sits. This word comes from the Latin navis, for ship — from which we get the navy. It is curious that the arches of a church’s ceiling often resemble the upside-down hull of a ship. Here in Omaha, one church — St. Thomas More — has always reminded me of a big boat. The huge wooden beams fit my mental image of Noah’s Ark.