What does prophecy mean?

Bible prophecy raises some tricky interpretive issues. That's hardly novel observation, to be sure. But I'm going to explore some issues that don't usually receive as much attention.

i) The grammatico-historical method generally regards authorial intent as a key element in grounding and ascertaining the sense of a passage. This can be complemented by other considerations, like the implied reader.

This also figures in the nature of inspiration. Take Luke's prologue or John's prologue. There the narrator is introducing the gospel in his own words. He's consciously choosing which words to use. Given a theory of verbal inspiration, God is controlling the process. Luke and John aren't aware of that. What they do is the result of that. 

The narrator chooses words to communicate the meaning he intends to convey to his readers. In that case, the connection between text and authorial intent is pretty direct. 

However, Luke and John (as well as Matthew and Mark) quote other speakers. Although they sometimes paraphrase their material, they aren't simply telling the story in their own words. When they quote someone else, they are transmitting the speaker's choice of words. 

In that case, it's not in the first place what the narrator means by those words, but what the speaker meant. He didn't choose their words. He's reporting their words. In that case, the connection between text and authorial intent is indirect. 

Of course, he's quoting them because they contribute to his narrative. At that level, authorial intent is still in play. What function do they serve in his narrative?

ii) Let's take visionary revelation, which often includes speakers within the vision. Take Revelation. When John emerges from his trance, he writes down what he heard. It's like he's taking dictation. He heard a character in his vision say something, and he passes that along to his readers. At that level, he's more like a scribe or messenger. He delivers the message. He didn't compose the message. I'm just discussing the quotations in Revelation. Obviously, John is responsible for much of the framing. 

In that case, to ask what John meant, what he was referring to, can be misleading. It's more a question of what the speaker had in mind, whom John is quoting. 

In theory, it's quite possible for messenger to have little or no understanding of the message he delivers. His role is confined to transmitting what someone else said or told him to say. 

iii) Further distinctions are possible. In Revelation, some speakers are arguably fictional characters, even if they represent real people. To take a comparison, I often dream about real people. People I know. But the people in my dream are fictional characters who stand for real people. The dream itself is a product of my own imagination, even though some people I dream have real-world analogues. 

If they say something in my dream, I'm writing the script. Those are really my words, which I'm putting on their lips. 

In a dream (unless it's a lucid dream), I'm not consciously choosing the words they use. This is subliminal. 

Of course, in the case of Revelation, we're dealing with inspired visions–unlike an ordinary dream. In principle, the seer could be the source of the words which speakers use. It would be the difference between consciously and unconsciously choosing vocabulary. When Luke penned his prologue, he consciously chose those words. Yet when John is quoting an angel in Revelation, it's possible that God inspired him to choose those words, but at a subliminal level–the way a dreamer is unwittingly scripting his own dream.

But let's take a different comparison. In Luke, the narrator quotes Gabriel speaking to Zechariah. One question is whether this is a subjective vision or objective vision. Did Gabriel appear to Zechariah in the sense that if you snuck into the sanctuary, you could see Gabriel conversing with Zechariah? That's one possibility. 

Or is this a subjective vision in which Zechariah underwent a trance. In that case you have a simulated angelic apparition. Yet Gabriel is still a real person who's choosing his own words. He controls his side of the dialogue. Same thing with the angel who spoke to Joseph in dreams. At that level, the statements mean what they were meant to convey by the speaker. 

iv) There are different ways to parse meaning. The words and sentences which a prophet uses have objective semantic content, even if (ex hypothesi) he doesn't understand the message himself. What is more, by divine providence and inspiration, working in tandem, the words are meant to correspond to an objective state of affairs, at some point in the future. 

v) If a prophecy is about the distant future, the description may be analogically true. By that I mean, a prophetic description of a modem city isn't going to depict the technological apparatus of a modern city. It won't describe cars, subways, traffic lights, skyscrapers, &c. An ancient oracle will use ancient descriptors which are analogous to their modern counterparts. 

It is, of course, possible, for God to give a seer a preview of the future. Enable him to actually foresee a modern metropolis. But he'd lack the modern vocabulary to match the scene.