Jesus spoke in parables so that only he that has faith understands the mysteries of God.
Example: note the following insight Jesus gives concerning understanding.
Matthew 16:5 And when his disciples were come to the other side, they had forgotten to take bread.
6 Then Jesus said unto them, Take heed and beware of the leaven of the Pharisees and of the Sadducees.
Notice that Jesus waits until the apostles are thinking about bread for their bellies before he warns them about the dangerous leaven.
He did this to reveal why carnal minds fail
to understand his parables.
7 And they reasoned among themselves, saying, It is because we have taken no bread.
Carnal minded people reason based on their unbelief towards Jesus. For, the unbelieving walk by sight and not by faith.
8 Which when Jesus perceived, he said unto them, O ye of little faith, why reason ye among yourselves, because ye have brought no bread?
Jesus perceived their unbelief and pointed out that “little faith” is what prevents spiritual understanding.
Notice that unbelievers reason among themselves in support of their collective false doctrines that are set contrary to God’s word.
And the conclusions reached by unbelievers are profoundly ignorant and even quite stupid.
9 Do ye not yet understand, neither remember the five loaves of the five thousand, and how many baskets ye took up?
10 Neither the seven loaves of the four thousand, and how many baskets ye took up?
Jesus points out that the apostles had seen Jesus feed thousands without having brought bread to feed them with.
This reveals that when men walk in unbelief of Jesus they are blind spiritually and can’t reason spiritually.
11 How is it that ye do not understand that I spake it not to you concerning bread, that ye should beware of the leaven of the Pharisees and of the Sadducees?
They failed to understand because they were walking in the flesh reasoning according to their bellies rather than according to God’s word.
This reveals that reasoning according to faith in God’s word is contrary to reasoning according to doubt.
I hear folks say they understand God’s word, but I find most Christians lack understanding, and few are corrected by God’s word.
Yet the unbelieving think they do understand.
They think that way because their eye isn’t single and so they reason two contrary ways and are in danger of mistaking the darkness of unbelief is enlightenment.
I find that Christians have difficulty understanding today because of having little faith in the written word of God.
Of course they have been taught in church to doubt the written word of God, and to instead reason like heathen scholars do.