Summary: Ultimately, the Lord makes people hear and will sort out the wheat from the chaff. That is not your job.
The last thing you need to know about the harvest is the Thresher. The harvest is all about the Lord and in this time He uses the Holy Spirit to bring about the fruit.
3 And he said unto me, Son of man, I send thee to the children of Israel, to a rebellious nation that hath rebelled against me: they and their fathers have transgressed against me, even unto this very day.
4 For they are impudent children and stiffhearted. I do send thee unto them; and thou shalt say unto them, Thus saith the Lord GOD.
5 And they, whether they will hear, or whether they will forbear, (for they are a rebellious house,) yet shall know that there hath been a prophet among them.
6 And thou, son of man, be not afraid of them, neither be afraid of their words, though briers and thorns be with thee, and thou dost dwell among scorpions: be not afraid of their words, nor be dismayed at their looks, though they be a rebellious house.
7 And thou shalt speak my words unto them, whether they will hear, or whether they will forbear: for they are most rebellious.
8 But thou, son of man, hear what I say unto thee; Be not thou rebellious like that rebellious house: open thy mouth, and eat that I give thee.
9 And when I looked, behold, an hand was sent unto me; and, lo, a roll of a book was therein;
10 And he spread it before me; and it was written within and without: and there was written therein lamentations, and mourning, and woe. KJV
I am not a five point Calvinist, by any means, but we know that in the foreknowledge of God He knows who will hear and who will not be it unsaved or saved people. Your job is to be the prophet. You are to do the speaking and not the winning. They need to know that a prophet was among them and you cannot do that unless you know your place and duty and His. If you turn them around or mix them you will be frustrated and lose more than you will gain. Just do what He asks in faith and faithfulness and leave the rest to Him.
Matt 13:30 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. KJV
He already knows that even in the Church there are going to be wheat and tares. Too many preachers want to tear up the tares and in the end often tear up the church and their ministry. Let them grow together. Preach the whole Word and the wheat will grow and the tares may leave your field and go to another willingly or they will expose themselves and will leave anyway though they are not as willing, but the shame will drive them out. If a few stay, consider them a means for your growth and no worse than Paul's thorn that made him rely upon God and not his own skill sets or gifts.
Rom 10: 1-21
1 Brethren, my heart's desire and prayer to God for Israel is, that they might be saved.
2 For I bear them record that they have a zeal of God, but not according to knowledge.
3 For they being ignorant of God's righteousness, and going about to establish their own righteousness, have not submitted themselves unto the righteousness of God.