That’s the challenge every art object makes: as you stand before it, what is it that you’re seeing? That doesn’t apply only to abstract works, or to some of the nonsense being passed off as contemporary “art”. “I’m seeing a beaker of urine,” you might say, “and frankly, I’d rather not.”
For many centuries, artists only had a couple of ways to make money. One was from wealthy patrons who would commission them to do portraits or works with mythological themes — a good excuse for the rich guys to have paintings of naked babes in their game rooms. The other potential source of income for, say, a painter in the 15th century, was decorative/devotional works for churches. In effect, these were Bible stories for illiterates. The faithful who came to services couldn’t read, but if the painter was skillful, the worshiper could see the drama of Jonah disappearing into the whale, or the anguish of Mary at the Deposition (taking Jesus down from the cross).
Over time, a “language” of symbols developed, one that painters learned and viewers came to understand. As we look at a medieval painting today, we know that the guys wearing gold frisbees on their heads are supposed to be saints. That’s part of the iconography, which is the fancy word for the subjects and symbols that constitute the characters of the language of religious painting.
You can usually assume that a woman holding a baby with a halo is probably the Virgin Mary, but another way to identify Mary is the color of her attire: in most cases she’ll be wearing red and blue. That practice began around the sixth century or so, and by the tenth century it had become part of the visual language. There are occasonal exceptions, but red and blue is the Mary tradition.
So who are those other people gathered around Mary in a painting we’ve encountered at a museum or a chapel? OK, if the man has a key (or keys) that’s Peter — a literal interpretation of Jesus granting to Peter the keys of the kingdom of heaven. A man holding what looks like a walking stick with a little cross on the top is John the Baptist. A woman holding a jar of ointment is Mary Magdalene, not a Mary Kaye cosmetics sales representative. If Andrew is in the painting, the clue is a transverse cross (X) on his person somewhere. By tradition, that was the means of his martyrdom.
The attributes of saints from post-Biblical times are often associated with the way in which they were martyred. Paintings of St. Lucy, for example, almost always show her holding a plate with her eyes on it. Just based on that, you can probably guess how she earned her palm frond. (A palm frond is often used as a symbol for a martyr.)
I could go on, but I sense your cursor finger starting to twitch. Next time you’re in a museum or gallery, though, take a moment to study that religious-themed painting. See if you can pick up any of the visual clues to the identities of the subjects. Ask yourself what certain enigmatic objects in the painting might symbolize. Either that, or skim the little plaque that’s beside the painting and quickly move on. That’s OK, too.