The time of separation the weeds from the wheat will come, when the angels, not men, will secure the wheat in barns. Then, as the workers reap the field, only the wheat will be united and secure. The weeds, apparently so plentiful, must first be gathered up and burned and can contaminate the wheat no longer. After the weeds are gathered they are taken to burn in the furnace. Jesus said the harvest is at the end of this world age and the reapers are the angels who will separate all that causes sin and all who do evil, they will be thrown into the fiery furnace.
Harvest is a common metaphor for the final judgement.
The Lord Jesus Christ will make the right distinctions at the end. The parable does not address the church situation at all but explains how the Kingdom can be present in the world while not yet wiping out all of its opposition. All must await the harvest. This deals with eschatological expectation. The tares represent worldly wisdom, pride, procrastination and they resemble Christians, but are Christless, moulding their character by Satan's prompting.