The larger version of this picture is in the Escorial in Madrid, and was probably intended for King Philip II.
El Greco made small copies of several of his own pictures to keep in his studio, of which this is probably one.
The subject is thought to be an allegory of the Holy League, a military alliance between Spain, the Papacy and the Venetian Republic, which was formed to combat the rise of Islam and the Turks.
The Pope, the Doge of Venice and Philip II are shown kneeling in adoration of the name of Jesus, shown in the heavens as IHS, these being the first letters of Jesus in Greek (IHSOUS).