"Alas, there are many who dwell among God's people at this time and have a name and a place among them who are sinners and not saints—hypocrites and not Believers—and these will, before long, be discovered and dismayed.
While all goes well with the Church of God, you cannot separate the vile from the precious, nor pluck up the tares from among the wheat, nor cast out the bad fish from among the good which are enclosed in the same net. But trying times come and days of adversity—and then the false brethren are discerned! When persecution arises, the hypocrites are offended! When affliction rushes like a torrent, the sand-founded houses fall! And especially shall it be so when, amid the terrors of the Last Tremendous Day, every secret thing shall be revealed—and hypocrites and sinners shall appear in their true colors!
Fearfulness will leap unexpectedly upon the hypocrites to their intense surprise, for they will see how impossible it is for them to dwell with God and to abide in His holy Presence. Oh, dear Brothers and Sisters, let us not be satisfied with being in Zion, or in the Church. Let us not rest till we are quite sure that we are not sinners in it, that we are not hypocrites in it, for, mark you, if our religion is not sanctifying and true, it will fail us in the hour of trial! If our confidence in God does not make us calm and hopeful in the time of temptation and sorrow, what is the use of it? Yet it is certain that no man shall find his profession to be of use to him in testing times but he that is true in it; he that is thorough in it; he that is neither a sinner nor a hypocrite in the sense in which those words are here used.
Safety in Zion belongs to those born in her by regeneration, reared in her by sanctification, enfranchised in her by faith in the Son of God, settled in her by fixed principles, confirmed in her by obedience to her laws and bound to her by intense love of her King and her citizens. Such "shall dwell on high" secure from danger—and only such—the aliens and foreigners within her gates shall, before long, be driven forth with shame!"
- CH Spurgeon, "The Rocky Fortress and Its Inhabitants".