24 Another parable put he forth unto them, saying, The kingdom of heaven is likened unto a man which sowed good seed in his field:
25 But while men slept, his enemy came and sowed tares among the wheat, and went his way.
26 But when the blade was sprung up, and brought forth fruit, then appeared the tares also.
27 So the servants of the householder came and said unto him, Sir, didst not thou sow good seed in thy field? from whence then hath it tares?
28 He said unto them, An enemy hath done this. The servants said unto him, Wilt thou then that we go and gather them up?
29 But he said, Nay; lest while ye gather up the tares, ye root up also the wheat with them.
30 Let both grow together until the harvest: and in the time of harvest I will say to the reapers, Gather ye together first the tares, and bind them in bundles to burn them: but gather the wheat into my barn.
Matthew 13:24-30
To make it a little easier, we also have Jesus's explanation later in this same chapter. Let me quote that below, and then I'll talk a little bit about it:
36 Then Jesus sent the multitude away, and went into the house: and his disciples came unto him, saying, Declare unto us the parable of the tares of the field.
37 He answered and said unto them, He that soweth the good seed is the Son of man;
38 The field is the world; the good seed are the children of the kingdom; but the tares are the children of the wicked one;
39 The enemy that sowed them is the devil; the harvest is the end of the world; and the reapers are the angels.
40 As therefore the tares are gathered and burned in the fire; so shall it be in the end of this world.
41 The Son of man shall send forth his angels, and they shall gather out of his kingdom all things that offend, and them which do iniquity;
42 And shall cast them into a furnace of fire: there shall be wailing and gnashing of teeth.
43 Then shall the righteous shine forth as the sun in the kingdom of their Father. Who hath ears to hear, let him hear.
Matthew 13:36-43
This is an interesting parable because it begins at the time of Jesus Christ, and the end is in the last days and has not yet occurred. So Jesus planted the good seed as he started his Church and soon thereafter it fell into apostacy as the tares began to grow.
The servants in the parable wanted to gather up the tares to protect the wheat. However the wheat was young (just as the Church in the Christ's time was young) and would be damaged greatly by the gathering of the tares. This is because tares and wheat are related crops. They look nearly identical as they grow, so it is hard to distinguish between them. It is not until they are ready for the harvest that they can be told apart. At this point you can cut them all down and separate them easily. This separation is a form of judgment that will be passed upon all people.
Are you a wheat or a tare? This question is perfect for self-reflection. I know that this parable prophesies of the future (which may be closer than we think- though no man knows). An interesting comparison, is that it is hard to tell if those around us are wheat or tares. This is why we should not judge others. Just as the Lord told his servants not to judge the wheat/tares and pluck out the tares, we must not judge our fellow men and identify people as "tares". We never know when someone will change and repent. We may have days when we ourselves behave more like tares than wheat, so we must be forgiving of others who also have "tare" days.
Lastly, we know that judgment comes. Even though it will be after the end of the world, if we die a "tare," there will be no time to repent thereafter. Now is the only time that we can repent and become wheat. So let us not judge others for it truly is impossible to see their hearts (only God looketh on the heart), and let us strive to be found as wheat at the last great harvest!