He put another parable before them, saying, “The kingdom of heaven may be compared to a man who sowed good seed in his field, but while his men were sleeping, his enemy came and sowed weeds among the wheat and went away. So when the plants came up and bore grain, then the weeds appeared also. And the servants of the master of the house came and said to him, ‘Master, did you not sow good seed in your field? How then does it have weeds?’ He said to them, ‘An enemy has done this.’ So the servants said to him, ‘Then do you want us to go and gather them?’ But he said, ‘No, lest in gathering the weeds you root up the wheat along with them. Let both grow together until the harvest, and at harvest time I will tell the reapers, Gather the weeds first and bind them in bundles to be burned, but gather the wheat into my barn.’”

Matthew 13:24-30 (ESV)

It is Jerome’s observation, that wheat and tares are so much alike in their first springing up, that it is exceedingly difficult to distinguish one from the other. . . . The difference (saith he) between them, is either none at all, or wonderfully difficult to discern, which those words of Christ plainly confirm. Let them both alone till the harvest; thereby imitating both the difficulty of distinguishing the tares and wheat; as also the unwarrantable rashness of bold and hasty censures of men’s sincerity or hypocrisy, which is there shadowed by them.

How difficult soever it be to discern the difference betwixt wheat and tares, yet, doubtless, the eye of sense can much easier discriminate them, than the most quick and piercing eye of man can discern the difference betwixt special and common grace; for all saving grace in the saints have their counterfeits in hypocrites. There are similar works in these, which is a spiritual and very judicious eye may easily mistake for the saving and genuine effects of the sanctifying Spirit…

And this difference will yet be more subtle and undiscernible, if I should tell you, that as in so many things the hypocrite resembles the saint; so there are other things in which a real Christian may act too like a hypocrite. When we find a Pharoah confessing, a Herod practising, as well as hearing, a Judas preaching Christ, and an Alexander venturing his life for Paul; and on the other side, shall find a David condemning that in another which he practised himself, a Hezekiah glorifying in his riches, a Peter dissembling, and even all the disciples forsaking Christ in an hour of trouble and danger: O then! how hard is it for the eye of man to discern betwixt chaff and wheat? How many upright hearts are now censured, who God will clear? How many false hearts are now approved, whom God will condemn?

Men ordinarily have no clear convictive proofs, but only probable symptoms; which, at most, can beget but a conjectural knowledge of another’s state. And they that shall peremptorily judge either way, may possibly wrong the generation of the upright; or, on the other side, absolve and justify the wicked. And truly, considering what hath been said, it is no great wonder that dangerous mistakes are so frequently made in this matter. But though man cannot, the Lord both can and will, perfectly discriminate them…

He will have a day perfectly to sever the tares from the wheat, to melt off the varnish of the most resplendent and refined hypocrite, and to blow off the ashes of infirmities, which have covered and obscured the very sparks of sincerity in his people: he will make such a division as was never yet made in the world, how many divisions soever there have been in it. “And then shall men indeed return, and discern between the righteous and the wicked; betwixt him that serveth God, and him that serveth him not.” Meanwhile, my soul, thou canst not better employ thyself, whether thou be sound or unsound, than in making those reflections upon thyself.

John Flavel, Husbandry Spiritualized; or The Heavenly Use of Earthly Things in Which Husbandmen Are Directed, p. 95-97