The rest of the parables weren't given an explanation in the Scriptures, and so we must search the Word of God to find out what they mean.
Matthew 13:31-32- Another parable put he forth unto them, saying, The kingdom of heaven is like to a grain of mustard seed, which a man took, and sowed in his field: Which indeed is the least of all seeds: but when it is grown, it is the greatest among herbs, and becometh a tree, so that the birds of the air come and lodge in the branches thereof.
The first thing to notice is that this is referencing the kingdom of heaven. That's the literal, physical kingdoms of this world. And, Christ already told us that the field that gets seed sown in it is the world.
What is the mustard seed? It's faith.
Luke 17:6- And the Lord said, If ye had faith as a grain of mustard seed, ye might say unto this sycamine tree, Be thou plucked up by the root, and be thou planted in the sea; and it should obey you.
This faith, however, is sown in the world. So that mustard seed that becomes a tree with the fowls of the air living in it is not a good thing! It has devils residing in it!
A mustard seed isn't suppose to become a tree. Mark tells it like this:
Mark 4:30-32- And he said, Whereunto shall we liken the kingdom of God? or with what comparison shall we compare it? It is like a grain of mustard seed, which, when it is sown in the earth, is less than all the seeds that be in the earth: But when it is sown, it groweth up, and becometh greater than all herbs, and shooteth out great branches; so that the fowls of the air may lodge under the shadow of it.
Notice this one speaks of the kingdom of God. The same parable, but with a spiritual twist. This shows you that it is a spiritual religious system that is spreading out and infection all areas of religion on the earth and corrupting them with evil.
The next parable is also pretty bad.
Matthew 13:33-35- Another parable spake he unto them; The kingdom of heaven is like unto leaven, which a woman took, and hid in three measures of meal, till the whole was leavened. All these things spake Jesus unto the multitude in parables; and without a parable spake he not unto them: That it might be fulfilled which was spoken by the prophet, saying, I will open my mouth in parables; I will utter things which have been kept secret from the foundation of the world.
Those that don't study Scripture want to say that this is the church spreading the gospel through the entire world. But this is not a positive parable.
What saith the Scriptures? Leaven is never a good thing in the Bible.
Matthew 16:6- Then Jesus said unto them, Take heed and beware of the leaven of the Pharisees and of the Sadducees.
Jesus warned the disciples to beware of leaven. He explains what this leaven is just a few verses later.
Matthew 16:12- Then understood they how that he bade them not beware of the leaven of bread, but of the doctrine of the Pharisees and of the Sadducees.
Luke 12:1- In the mean time, when there were gathered together an innumerable multitude of people, insomuch that they trode one upon another, he began to say unto his disciples first of all, Beware ye of the leaven of the Pharisees, which is hypocrisy.
He defines leaven as hypocritical false doctrine.
Then He goes one step further.
Mark 8:15- And he charged them, saying, Take heed, beware of the leaven of the Pharisees, and of the leaven of Herod.
The disciples argued among themselves as to what this could mean, and I believe Paul tells us.
I Corinthians 5:6-8- Your glorying is not good. Know ye not that a little leaven leaveneth the whole lump? Purge out therefore the old leaven, that ye may be a new lump, as ye are unleavened. For even Christ our passover is sacrificed for us: Therefore let us keep the feast, not with old leaven, neither with the leaven of malice and wickedness; but with the unleavened bread of sincerity and truth.
Leaven is false doctrine, hypocrisy, malice, and wickedness. These things have no place in the body of Christ! They aren't good things that should define Christianity. That's why Jesus said "Beware"! Because a little leaven will eventually corrupt the entire thing.