My seminary professors drilled into me that the meaning of any Bible text should be anchored in the original author's intent in writing it.

This has been a good discipline for me. The biblical authors were far more godly than I am, so who am I to go beyond what they intended to communicate. But it has always left me wondering, "Can there be meanings the original author did not intend? Could Rahab's scarlet cord point to the blood of Christ, even if the author of Joshua didn't intend it?"

Most Christians have said "yes", since the primary author of Scripture is the sovereign and omniscient Spirit. He can work above and beyond the intentions of the human author, and likely did so many times.

But there is another reason why texts could have deeper meanings that the author didn’t anticipate. I have often found that people get insights out of my sermons that I didn't intend. They say, "I love that part when you said this..." But I never said that. Their insight was a good one, and definitely a worthy take-away from the sermon. What happened? They found a true meaning that I didn't intend. The reason this happens is because my sermon was built on a Scripture passage that was itself loaded with meaning that I didn't put there. So I carried into my sermon many insights I wasn't aware of.

The biblical authors are doing the same thing. They are constantly alluding to previous biblical authors, covenants, promises, types, stories, saints. Each is rich with insights and meaning, more than any human could fully know. So they too carry into their writings meaning beyond their knowledge.

CS Lewis says all art is like this. There is no such thing as pure originality, because everything we write or make is using materials created by God. Those materials have meanings he has woven into them, often meanings of which we are unaware. So anything we make or write will always have meanings we didn't intend, and yet those meanings are still legitimate. It is the same with the biblical authors. (By the way, this is not relativism. It doesn't mean all interpretations of writing or art are legitimate. Readers must respect both the author and the materials and not project their own feelings onto the text, assuming it can mean whatever they want it to. There can definitely be interpretations that are wrong. We can trust God never intends a meaning not in harmony with the Bible and the faith once for all delivered to the saints.)

I’ll end with how Lewis said it in a letter, which is much better than I could in any format:

"'Creation' as applied to human authorship (I'm on your first letter now, you see) seems to me an entirely misleading term. We make ex hypokeimenon. i.e. we re-arrange elements He has provided. There is not a vestige of real creativity de novo in us. Try to imagine a new primary colour, a third sex, a fourth dimension, or even a monster wh. does not consist of bits of existing animals stuck together. Nothing happens. And that surely is why our works (as you said) never mean to others quite what we intended: because we are re-combining elements made by Him and already containing His meanings. Because of those divine meanings in our materials it is impossible we shd ever know the whole meaning of our own works, and the meaning we never intended may be the best and truest one." (Letters of C. S. Lewis, p. 371, to Sister Penelope)