24 Jesus told them another parable: “The kingdom of heaven is like a man who sowed good seed in his field. 25 But while everyone was sleeping, his enemy came and sowed weeds among the wheat, and went away. 26 When the wheat sprouted and formed heads, then the weeds also appeared.
27 “The owner’s servants came to him and said, ‘Sir, didn’t you sow good seed in your field? Where then did the weeds come from?’
28 “‘An enemy did this,’ he replied.
“The servants asked him, ‘Do you want us to go and pull them up?’
29 “‘No,’ he answered, ‘because while you are pulling the weeds, you may uproot the wheat with them. 30 Let both grow together until the harvest. At that time I will tell the harvesters: First collect the weeds and tie them in bundles to be burned; then gather the wheat and bring it into my barn.’”
Dark Disciples
It seems that God allows dark things to happen in the church and sinister people to move among his disciples. Jesus had a disciple whose heart was gripped by Satan. Judas Iscariot betrayed Jesus for silver coins. I heard how a student of mine was betrayed when her pastor was convicted of killing his business partner in a car crash and was sent to jail. In this parable the grass that grows among the wheat looks like wheat but does not bear the same fruit. In fact the fruit of this grass is poisonous. If God were to weed out such ‘disciples’ from among the true disciples though, damage would be done to the whole harvest. It is at the end of time, before the judgement throne, that a person’s heart will be revealed.
Questions
- Who plants weeds?
- How might the previous parable and this one be related?
- How does this parable fold in end times?
- What kind of person might be a false or dark-hearted disciple?
- Why do you think that we have this parable for believers?
Plymothian 
As you say, these weeds look like the real deal. But they aren’t. They are certainly harmful to the wheat. But the owner knows that it will do even more damage to the wheat if he removes them. Is there a sense in which the presence of the weeds causes the wheat’s roots to work harder, to press deeper? I don’t know.
I think this parable is there to remind that we ultimately must follow God’s truth. If we question a fellow believer, a leader of the church, etc we need to remember that the place for answers is in the bible. We should not just follow people because they are leaders of the church but be okay questioning things that feel morally wrong.