Joel 3:14 (NKJV)
14 Multitudes, multitudes in the valley of decision!
For the day of the Lord is near in the valley of decision.
2 Thessalonians 2:1-3 (NKJV)
1 Now, brethren, concerning the coming of our Lord Jesus Christ and our gathering together to Him, we ask you,
2 not to be soon shaken in mind or troubled, either by spirit or by word or by letter, as if from us, as though the day of Christ had come.
3 Let no one deceive you by any means; for that Day will not come unless the falling away comes first, and the man of sin is revealed, the son of perdition,
4 who opposes and exalts himself above all that is called God or that is worshiped, so that he sits as God in the temple of God, showing himself that he is God.
These two things will happen before the day of the Lord; Many people will be in the valley of decision, both believers and unbelievers deciding whether to serve God or Satan. As a result, there will be a great falling away of believers, especially lukewarm believers, but there will also be unbelievers saved during this time.
Joel 2:1-2 (NKJV)
1b For the day of the Lord is coming, for it is at hand:
2a A day of darkness and gloominess, a day of clouds and thick darkness,
John 9:4 (NKJV)
4 I must work the works of Him who sent Me while it is day; the night is coming when no one can work.
The darkness is coming. God's people who are walking in the light need to lead others, both believers and unbelievers, to Christ who is the Light of the world while there is still time, before the dark night of tribulation comes suddenly when no man can work!