So why did Christ speak in parables?
And when he was alone, they that were about him with the twelve asked of him the parable. And he said unto them, Unto you it is given to know the mystery of the kingdom of God: but unto them that are without, all these things are done in parables:
And he also taught them other things in private. And they taught those who followed them, things both written and not. And all this is part of the Apostolic tradition, the entirety of Jesus’ revelation: the deposit of faith.
It is not hidden or secret, it is taught freely by the Church.