The meaning of this scripture is very simple if you allow the other scriptures concerning the kingdom to interpret it. All that's being said hear is that "there is nothing hid which shall not be manifest". It's an example of how the word of God reacts with the human spirit and together they radiate the fact that his word was put in. If you take two balls of dough, insert yeast in one of them and come back in twenty minutes, it doesn’t take a genius to say "hey someone put yeast in that one". Yeast is not good or bad it's just a catalyst that works with something else for a desired end. Certainly it can be bad, "beware of the leaven of the scribes and Pharisee’s-hypocrisy" for there is nothing covered that shall not be revealed (same idea). But it also says that the kingdom of God is like leaven.
The meaning is this. When we "hide" the word in our hearts, the leaven of god’s word will work with our spirit to "manifest" or bring to light or "reveal" the fact that we "sowed" to our hearts the word. It will manifest. Now, if there's nothing hid that shall not be manifest, shouldn't we as Christians be asking "then how on earth do I "hide" something? This is the idea here. We have a treasure hid in our hearts, and the person who discovers how to hide something, will be able to "manifest" or tap into that hidden treasure. He'll bring forth fruit.