If we believe Mark, the disciples were a bit thick-headed. Jesus complains they don't understand. Jesus, at times, seems exasperated with them. They try to take his parables literally and get confused by their own confusion. At one point, Jesus says he teaches in parables but teaches the deeper explanations to the disciples in private. But we don't really have any of these private teachings. Probably the disciples didn't understand them either, so it's just as well.
The nature of parables, myths, poetry etc is surplus meaning. When Robert Frost wrote, Two roads diverged in a yellow wood..., for example, he was not talking about a specific yellow wood. When he declared he took the one less travelled, he wasn't talking about a hike in the woods and a Y in a specific path. When the Psalmist wrote the beautiful songs, they were poetry with surplus meaning, way beyond literal.
The purpose of surplus meaning is to make us think, to think about what this parable/poem means in our life, to consider it from all sides. It is not possible for it to have only one meaning. It has a universalness to it that can speak to a first century peasant, a medieval monk, the titan of industry, man and woman from all ages and all strata of society.
Make an experiment for yourself. Pick a parable to live with for one week. Read it every morning and every evening. Roll it around in your mind and heart. Take notes. At the end of the week, read over your notes and see a part of the parable's mystery that has unfolded for you. There is more for the Divine Mystery is infinite. The journey into The Mystery is thrilling each step of the way.
God walks with you.