What does Matthew 13:27 mean?

Jesus is telling a story, a parable, about an attack on a farmer's field of wheat (Matthew 13:24–26). Later He will explain to His disciples exactly what each element in the story represents (Matthew 13:36–43).

Shortly after the farmer planted his crop, an enemy snuck into his field under the cover of darkness and planted weeds alongside his wheat. Bible scholars understand this weed to be "darnel," also known as "tares." This is a poisonous ryegrass that looks so similar to good grain that it is sometimes called "false wheat." The difference only becomes noticeable once the wheat plants begin to bear grain. By then, the root systems of the two plants would be intermixed in the soil. This kind of sabotage is a known tactic in agriculture, meant to devastate someone else's harvest.

The servants responsible for tending the fields eventually notice that these weeds are growing up alongside the otherwise healthy grain. They take their observation to their master, the farmer, along with pointed questions: How is this happening? Didn't you use good seed? If so, where did these weeds come from? The servants responsible for taking care of their master's field want to know where the process broke down. Despite what some interpreters claim, Scripture doesn't blame the field workers for letting this happen.