And when the king came in to see the guests, he saw there a man which had not on a wedding garment… – Matthew 22:11

Whenever there is a revival and many are brought to Christ, it seems inevitable that at the same time a proportion of unworthy persons should enter the church. However diligent may be the oversight there will be pretenders creeping in unawares who have no true part or lot in the matter, and hence, when the preacher is most earnest for the ingathering of souls to Christ, he needs to couple therewith a holy jealousy, lest those who come forward to make a profession of faith should be moved by carnal motives, and should not really have given their hearts to God. We must use the net to draw in the many, but all are not good fishes that are taken therein. On the threshing floor of Zion the heap is not all pure wheat, the chaff is mingled with the grain, and therefore the winnowing fan is wanted. God’s furnace is in Zion, and there is good need for it, for the gold is yet in the ore and needs to be separated from the dross. Wood, hay, and stubble building is quick work, but it is a waste of effort; we need continually to examine our materials, and see that we use only gold, silver, and precious stones. It is most needful in times of religious excitement, to remind men that godliness does not consist in profession but must be proved by inward vitality and outward holiness. Everything will have to be tested by a heart-searching God, and if, when He comes to search us, we are found wanting, we shall be expelled even from the marriage feast itself; for there is a way to hell from the very gates of heaven. In a word, it is well for all to be reminded that the enemies of the great King are not only outside the church, but they are even in it; while a part refuse to come to the wedding of His Son, others press into the banquet and are still His foes. May God grant that this subject may have a heart-searching effect. May it be as the north wind when it blows through the marrow of the bones. May it lead us to desire to be searched and tried of God, whether we are truly in the faith, or are reprobates in His esteem. ~ C.H. Spurgeon

https://www.blueletterbible.org/Comm/spurgeon_charles/sermons/0976.cfm