Zechariah 13:8-9

And it shall come to pass, that in all the land, saith the Lord, two parts therein shall be cut off, and die; but the third shall be left therein. 9 And I will bring the third part through the fire, and will refine them as silver is refined, and will try them as gold is tried: they shall call on my name, and I will hear them: I will say, It is my people: and they shall say, The Lord is my God.

There will be a sifting time in the Church, not for the terror or trial of the real Church of Christ, for the Lord knoweth them that are his. But this trial is for the discovery of nominal Christians from true believers. All the scriptures declare concerning this time, And Jesus himself left it in testimony with the beloved Apostle John. Rev_2:8-10; Rev_3:7-13. The Lord will also try and exercise the graces of his Holy Spirit he hath given them, with afflictions and various trials. And this is what is meant by bringing them through the fire. But then let the Reader be careful to observe, (for it is an important, observation), that these trials of God's faithful people are never made by way of discovery, whether they are or are not his people, for known unto God are all his works from the beginning; but purely that they may be conformed to the image of their glorious head. See those two striking scriptures to the point. Romans 8:29 and Isaiah 48:10. Reader! it is a grand point in Gospel truth, to stand confirmed in this glorious doctrine, that in Christ the Church is beheld and accepted; and therefore God brings his redeemed into exercises for furtherance in grace, and not to prove what is already known, whose they are; for this would be to rest the final consequence of grace upon man's obedience, and render uncertain Christ's merit and death. Blessed be God! salvation hath more sure ground to rest upon. The Prophet expresses the blessed covenant, in the full terms of it, when running it up to the fountain head: I will say, saith God, it is my people; and they shall say, the Lord is my God.