First the kingdom was sown by the planter as discussed here. The seed, according to Wiersbe, is the Word of God which is "living and powerful" (Heb. 4:12). "The truth of God must take root in the heart, be cultivated, and permitted to bear fruit" which is the result of true salvation. Fruit includes things such as holiness, good works, Christlike character, worshiping God and so forth.
As we learned a lot of the seed never produced fruit. Only that which fell upon good soil was fruitful.
The rest of Matthew 13 contains six parables that begin with "the kingdom of heaven is like." It includes
1. wheat in a field growing alongside weeds which will be separated at harvest
2. a mustard seed which grows into a large plant
3. leaven or yeast in dough
4. a hidden treasure
5. a pearl of great value
6. a fishing net which gathers good and bad fish which will be separated
Wiersbe suggest the first three parables "reveal that Satan is primarily an imitator: He plants false Christians, he encourages a false growth, and he introduces false doctrine." He also believes the hidden treasure represents Israel, the pearl is the church and the fishing net represents the saved Gentile nations who will enter the kingdom. His views on those things are rather interesting, but they are much further symbolic than I've ever taken them to be. I've tended just to take the parables more as symbolic of the kingdom of heaven since that's what Jesus was talking about.
This chapter ends with Jesus returning to his hometown, the people marveling at his miracles and words then being offended by him because apparently they were unwilling to believe a local boy could grow up to be as wise and wonder-working as this Jesus seemed to be.
53When Jesus had finished these parables, he moved on from there. 54Coming to his hometown, he began teaching the people in their synagogue, and they were amazed. "Where did this man get this wisdom and these miraculous powers?" they asked. 55"Isn't this the carpenter's son? Isn't his mother's name Mary, and aren't his brothers James, Joseph, Simon and Judas? 56Aren't all his sisters with us? Where then did this man get all these things?" 57And they took offense at him.
But Jesus said to them, "Only in his hometown and in his own house is a prophet without honor."
58And he did not do many miracles there because of their lack of faith.
I wonder why it was such that a prophet was without honor in his own hometown. Notice Jesus didn't do many miracles there. Their lack of faith deprived them of what he was able to do. God likes our faith!
Warren Wiersbe in The Bible Exposition Commentary, Volume I, pg. 45-48