The image above is a representation of, as its inscription says, the Sozhestvie Svyatago Dukha Na Apostolov — “The Descent of the Holy Spirit Upon the Apostles.” The Greeks call this type Η Πεντηκοστή — He Pentekoste, pronounced “ee pen-tee-kost-EE” in modern Greek. It means “fiftieth,” — in this case the 50th day after Easter.
So it is a type found in both Greek and Russian iconography, one of the major church festivals.
The type depicts the descent of the Holy Spirit upon the Apostles on the Day of Pentecost, as described in the second chapter of Acts. At the top of this image is a descending flame — the fire of the Holy Spirit. Some examples show individual tongues of flame resting on the heads of the Apostles. The icon takes some liberty, however, in placing the later apostle Paul across from the apostle Peter at the top of the group; Paul was not present at the “descent,” but was added in iconographic convention nonetheless. Also Mary is included at the head of the Apostles in the above example, though she is omitted in many others, leaving the chief seat empty — the situation of the Apostles after Jesus ascended and before the Holy Ghost descended upon them as their comforter and teacher. In Greek icons, the youngest apostles are often placed in the two lowest seats.
The stylized background buildings — called “palaces” in Russian icon-painting terminology — here represent the Upper Room in which the Apostles were seated.
At the base of the type is a completely symbolic image, an old man in a dark space sometimes shown as a cave, though here it is just an arched opening, In Greek icons he bears the name Ο Κόσμος — Ho Kosmos — “The Cosmos,” meaning “The World.” He is in the darkness of the world without the Gospel, and aged by sin, but in his hands he holds a cloth. Though not shown here, there are often twelve rolled scrolls lined up on the cloth, which represent the promise of the coming of the teaching of the Twelve Apostles to the world, now that the Holy Spirit is descending. Photios Kontoglou (1895-1965), the fellow who inspired a revival of the “Byzantine” style of icon painting in Greece, calls the cloth held by the old man the “sindon,” which refers to the burial shroud of Jesus. The message is that the death and resurrection of Jesus led to the descent of the Holy Spirit and the going forth of the teaching of the Twelve Apostles into all the world.
An observant reader asked why old “Cosmos” in the first icon shown above has a halo. The answer is that it was a painter’s error. He did not understand the symbolism or tradition of the type, and mistakenly thought that the symbolic representation of “The World” was a saint of some kind, so he gave “Cosmos” a halo, but without a name written in it. Other icons of the same type (like the second image) correctly show “Cosmos” with no halo.