A couple of thoughts from Mark 4:20-22:
"'But those that were sown on the good soil are the ones who hear the word and accept it and bear fruit, thirtyfold and sixtyfold and a hundredfold.' 21 And he said to them, 'Is a lamp brought in to be put under a basket, or under a bed, and not on a stand? 22 For nothing is hidden except to be made manifest; nor is anything secret except to come to light.'"
(1) The "fruitfulness" of the seed in this fourth soil is connected with the production of more seed. It's as if Jesus is saying that the fruitfulness of his word in us is connected with more of his word coming from us.
(2) This is evidently what the word of God is for. Just as a lamp is designed not to be put under a bed or under a basket, but on a stand where it can be seen; so also the word of God is designed to be proclaimed by those who receive it.