Matthew presents a portrait of Jesus as the Christ, showing how the ministry, death and resurrection of Jesus is tied together with his role as Messiah. However, what separates Matthew from the other Gospel writers, is the focus on the church, its way of life in response to the message of Jesus.
In Matthew chapter 13 verses 24 to 30 we have the parable of the weeds. It is similar in focus to the parable of the sower. The message here is carry on your work faithfully in spite of mixed results. However, the results you achieve will be judged by God on Judgment day.
In verses 36 to 43 of chapter 13, we have an interpretation which does not come out of the tradition of the church but from the author, Matthew. Verse 41 gives us a clue about the author's purpose, The phrase Kingdom of the son of man is the church. It is contrasted with the kingdom of the father in verse 43. At present the church is a mixed body, containing both good and bad. These individuals will be judged by god at the end of the age. They are not to be judged by the church in this present time.