Numbers 19:20
But the man that shall be unclean, and shall not purify himself, that soul shall be cut off from among the congregation, because he hath defiled the sanctuary of the LORD: the water of separation hath not been sprinkled upon him; he is unclean.
The verse warns that the man who is unclean and will not purify himself shall be cut off from among the congregation, and to be thus cut off is to be lost. The cutting off comes because he has defiled the sanctuary of the Lord, the water of separation not having been sprinkled upon him. Applied spiritually, the unclean are those who persistently resist heavenly light and cherish opposition instead of being cleansed. In particular they are those who have stood for years hating and despising the messengers of God's righteousness and the message of salvation only through the merits of Jesus Christ and the grace of the Holy Spirit. Unless they speedily humble their hearts before God and confess their many sins, going on only a little longer in rejection of light from heaven leaves them cut off as fighters against God.
Those who refuse to humble themselves, confess their sins, and accept cleansing will be lost, and conviction that comes too late will only expose their opposition to God. The warning therefore calls for careful self-examination that each Christian may know his own weakness, and for revival and reformation so that ministers and laypeople reach a higher standard of righteousness.