Book of Joel Chapter 2 Vs. 31

 The Lord Will Pour Out His Spirit

The sun shall be turned into darkness, and the moon into blood, before the great and the terrible day of the LORD come. Joel 2:31

The sun shall... Not by eclipses, as Aben Ezra; but by the clouds of smoke arising from the burning of towns and cities. Which would be so great as to obscure the sun, and through which the moon would look like blood.

before the great... Joel 2:30-32 proves that the Holy Spirit will be poured out upon all flesh, and people will continue to be saved during the future tribulation period, for these signs will take place only during that time and before the great and awesome day of the Lord (Acts 2:16-21).

The days of our life are our days wherein we do what we please; that will be the "Day of the Lord," when He, our Judge, shall require the account of all our doings. It will be "great," because it is the horizon of time and eternity; the last day of time, the beginning of eternity. It will put an end to the world, guilt, deserts, good or evil.

It will be "great," because in it great things will be done. Christ with all His Angels will come down and sit on His Throne; all who have ever lived or shall live, shall be placed before Him to be judged; all thoughts, words, and deeds shall be weighed most exactly; on all a sentence will be passed, absolute, irrevocable throughout eternity.

The saints shall be assigned to heaven, the ungodly to hell. A great gulf shall be placed between, which shall sever them forever. So that the ungodly shall never see the godly nor heaven nor God; but shall be shut up in a prison forever, and shall burn as long as heaven shall be heaven, or God shall be God.

"That day shall be great to the faithful, terrible to the unbelieving; great to those who said, 'Truly this is the Son of God;' terrible to those who said, 'His blood be upon us and upon our children."

"When then thou art hurried to any sin, think on that terrible and unendurable judgment-seat of Christ, where the Judge sits on His lofty Throne. And all creation shall stand in awe at His glorious Appearing and we shall be brought, one by one, to give account of what we have done in life.

Then by him who hath done much evil in life, there will stand terrible angels. "There" will be the deep gulf, the impassable darkness, the lightless fire, retaining in darkness the power to burn, but deprived of its rays. There is the empoisoned and ravenous worm insatiably devouring and never satisfied, inflicting by its gnawing pangs unbearable. There that sharpest punishment of all, that shame and everlasting reproach. Fear these things; and, instructed by this fear, hold in thy soul as with a bridle from the lust of evil."

Mark 13:24-25 "But in those days, after that tribulation, the sun shall be darkened, and the moon shall not give her light," "And the stars of heaven shall fall, and the powers that are in heaven shall be shaken."

The very best thing a Christian can do, is be ready to meet their Lord. We are not to fear these things, but rejoice when they happen, because our redemption is near.

Luke 21:28 "And when these things begin to come to pass, then look up, and lift up your heads; for your redemption draweth nigh."

Blood and fire and billows of smoke suggest the effects of warfare. The turning of the moon to blood refers in a poetic way to its being darkened (cf. the parallel line, The sun will be turned to darkness, and Joel 2:10; 3:15). Though such phenomena will signal doom for God’s enemies, His people should interpret them as the precursors of their deliverance (cf. Mat. 24:29-31; Mark 13:24-27; Luke 21:25-28).