Jesus clearly gave answers to His disciples as it pertains to their protection as True Christ Followers.
During His 3/12 ministry on the earth- it was His mission and that of the Father to make clear what The Kingdom of God was and was not.
Likewise, Jesus used Parables ( to conceal truth) to make His teachings clear to His disciples, however- not the crowds. Such Parable of The Wheat and Tares, was used to inform, His disciples on the revealing of The Kingdom of God and the enemy that opposes it.
In the Parable of The Wheat and the Tares- Jesus took His time to make known a very key understanding of what would be known not only to His disciples then, but His disciples now, what would be and who would rage war against them and His Kingdom.
The Tares as Jesus explained to His disciples were "sown into" the world- Satan's system of things. The enemy "systems" and those who would be planted in to destroy and oppose the work and real Mission of The Father.
Jesus gave instructions to "leave them be" as it would be more harm to remove them. This no doubt would pose a very threatening presence for His true disciples. Yet, Jesus did not leave them clueless on how to identify them.
There are TWO VERY DISTINCTIVE Elements in Identifying tares:
1) They will not hear your Words -John 8:47 2) They do not carry or bare, a true witness to The Spirit of Prophecy! -Revelation 19:10