Mathews addition of the parable of the weeds expands upon Marks parable of the seeds to better show the destruction of the followers of Jesus by just one bad seed, or the weeds. In Mathew 13:37-40 its stated, “The one who sows the good seed is The Son of Man; the field is the world, and the good seed are the children of the kingdom; the weeds are the children of the evil one and the enemy who sowed them is the devil; the harvest is the end of the age, and the reapers are the angels”. So, as stated above, it only takes one “enemy” to sow a bad seed in the field and corrupt the the growth of the good seeds or the children of God. I believe the addition of Mathews parable of the weeds effects his description of Jesus because this shows in a way that Jesus is warning us against Gods judgment. Just as the harvester and the reaper, the angels, will separate the weeds from the wheat and throw the weeds in the fires of the furnace, God will do the same at the final judgment, he will separate the truly good and truly evil and the truly evil will burn in the fires of Hell.
I think the parable of the treasure and the pearls is Jesus trying to represent how important the kingdom of Heaven truly is because once we know of it we would give up everything in order to possess it. In the two parables the man gives up everything he has to get the kingdom. I think the catch is that the in both the parables the treasure and the pearl are hidden, so that is trying to represent how many people miss the word of Jesus and the chance to possess the ability to enter the Kingdom of Heaven. Maybe on of the reasons these two small parables are “sandwiched” between the parable of the weeds and the net is because both these two parables talk of the evil being “weeded” out by the angels either in the term of weeds or fish and being “ thrown into the furnace of fire, where there will be weeping and gnashing of teeth” (Mathew 13:50). The treasure and pearl parable is almost the explanation of how to avoid the fires of the furnace, in terms of search for the treasure of the Kingdom of God and you shall receive it.