It is so

(1) Because our Lord states it in the Gospels, the Holy Spirit repeats it in nearly very Epistle, it is the basis of the promises and threats to the Seven Churches, and it is foretold as an actual experience in the prophecies of the Apocalypse. 

• Matthew 7:21; Luke 20:35; etc.
• Ephesians 5:5,6;  Galtions 5:19-21
• Revelation 2 and 3
• Revelation 11:18, 20:6

(3) Because the Age to Come- as distinct from the Eternal State, which is based on grace alone (Rev. 20:15)- is revealed as "one last day of a thousand years, a full and perfect judicial aeon," in which all seed sown in this Age reaps its exactly corresponding harvest, and to which all adverse consequences of works done after faith are confined.

(4) Because it safeguards the infinite merits of our Lord's imputed righteousness and divine sacrifice by establishing the spotless and eternal standing of every believer in Him while it also safeguards human responsibility and divine justice by making every believer accountable for his own walk, under pain of a possible forfeiture of coming glory.

(5) Because - since God's dealings with His people must always rest on the character of God, and God's character is not mercy only, but justice also, it is inconceivable that a disciple's life, if unholy, should have no profouinder effect on his destiny than mere gradation in glory. 

(6) Because, if we acknowledge any judgment of a believer's works at all, and that before a tribunal which is a judgment seat and not a mercy seat, we are thereby compelled to acknowledge, further, that the investigation must be strictly judicial, and that it will therefore be as exactly graded in censure as it is in praise. 

(7) Because it vindicates the holiness and justice of God from the charge of compounding with His people's sins, and makes the highest glory given by God to rest only on the active righteousness of the disciple co-operating, consistantly and ceaselessly, with the imputed righteousness of his Lord, - obedience being the only proof of love. 

(8) Because it is the supreme reconciliation between Paul and James, that is, between justification through faith unto Eternal Life, and justification through works unto Millennial Reward;  for into an Everlasting Kingdom, which is granted as a gift, and abundant entrance can only be a prior one, and it is built upon a sevenfold foundation of works. (2 Pet. 1:5-11)

(9) Because it is perhaps as near an approximation as has yet been reached to a solution of the perennial controversy between the Calvinist and the Arminian: for it establishes all the passages of glorious certainty, while it leaves ample scope for the most solemn warnings: it takes both sets of Scripture  as it finds them. 

(10) Because it gives the natural and unforced interpretation to the facts of Church life, as it does also to the simple statements of HolyWrit, and reveals how exactly the one squares with the other, both in present character and in just recompense; and whether as selective rapture, or exclusive resurrection, or forfeiture of crowns, or failure of the prize, or conflagration of works, or limited coheirship, or even penal consequences, - the argument is cumulative, and overwhelming in its accumulation. 

(11) Because large sections of the Church of God are purged, and can only be purged by seeing the drastic consequences of a carnal life;  and because, for want of a frank and fearless statement of these consequences, multitudes of disciples are now wrapt in a profound slumber. 

One last application of the principle, and the most immedite and urgent, still remains:

It is the peril of unwatchfulness on the near approach of the last judgments.  "All these things that shall come to pass" (Luke 21:36): 

What things?

Crowding and disastrous miracles: terrors from heaven;  signs in sun and moon and stars;  the powers of heaven shaken; for these will be the days of vengeance, of persecution, of distress of nations, men fainting for fear,.  "Then shall be great tribultion, such as hath not been from the beginning of the world until now, no, nor ever shall be" (Matthew 24:21)

No peril so awful has ever demanded an escape so great.

Escape IS possible:  "to escape all these things."  Now since the distress is universal it can only be an escape into the heavens; "for it shall come upon all them that dwell on the face of all the earth."    No foothold of safety will exist in the whole inhabited world.  It is an escape to "the Son of Man coming in a cloud with power and great glory":  for "He bowed the heavens also, and came down; He sent from on high, He took me"  (Psalms 18:9)

Therefore this cannot be the deliverance of the elect Jewish remnant: becuse...
(1) the escape of the Jew is into the wilderness, never into the heavens (Rev. 12:6).  The earthlyescape was typed byNoah passing through the Flood, the heavenly by Enoch who escaped it altogether;  and this is an escape which sets "before the Son of Man".
(2) The Jewish escape is active:  this escape is passive.  The faithful Jew is to 'flee to the mountains' (Matthew 24:16) the faithful disciple here is to prayto be removed-- "to be set" ['by angels,'] before the Son of Man." 
(3) The Jewish escape is on purely physical grounds, if he instantly sets his face to the mountains, whatever his exact moral condition, he escapes: but this deliverance turns critically on moral acceptablilty-- "accounted worthy to escape." 

Other scriptures are conclusive that this escape is Christian.

(1) To the chief officer of a Christian church is our Lord's promise: "Because thou didst keep the word of my patience, I also will keep thee from the hour of trial, that hour which is to come upon the whole world" (Rev. 3:10) 
(2) To the chief officer of a Christian church is also our Lord's warning: "If therefore thou shalt not watch, I will come as a thief, and thou shalt not know what hour Iwill arrive over thee" (Rev. 3:3). 
Thus if, on the ground of 1 Thess. 5:4, it should be said that the Parousia cannot overtake a believer as a thief, this word of our Lord at once negatives the inference, for the threat of a thief-like descent, accompanied by total ignorance of the arrival, is addressed to a Christian pastor. 
(3) The Type exquisitely confirms it. The Field is the world; the Wheat is the church; the Reapers are angels (Matthew 8:39): the Reapers first of all gather the First fruits, then garner the Harvest, and finally glean the Corners of the Field which had been diliberately left unreaped (Lev. 23:10-22) 
So first fruits are found in the Heavenlies before the harvest (Rev. 14:4) and afterthe harvest (Rev. 16:15) the warning to watchfulness still goes forth...(Rev. 14:15).  "Only those who are devoutly looking and waiting for the Saviour's return shall be taken at first" (Seiss).

The moral crisis of the escape lies in the condition: "watch ye at every season, making supplication, that ye may prevail to escpe" (Luke 21:36) [so you can escape]
These Divine words, if they have anymeaniong at all, must mean that without the worthiness the escape is impossible: and without the prayerful vigil the worthiness is impossible: "watch and pray always."  "No command is more frequent, none more solemnly impressed" (Dean Alford):  for the escape is no privilege attached to faith, but a reward attached to a standard of holiness known only to God.  "Then shall two men be in a field; one is taken, and one is left: two women shall be grinding at the mill; one is taken, and one is left.  Watch therefore: for ye know not on what day your Lord cometh" (Matthew 24:40) "Our Lord assumes that some of His beloved Church will continue to be cared for as His sheep upon earth, until He destroy 'that wicked' with the breth of His mouth" (Tregelles). 
"Watch" is one of the great comprehensive words of the Bible. Watch oneself:  watch for flying opportunities: watch for dying souls:  watch Satan: watch God.  Watchfulness is acute alertness exercising every faculty for God.  But it must be accompanied by specific prayer: "pray that ye may be accounted worthy";  "that ye may prevail to escpe."
Watchfulness invokes all our powers for God, prayer invokes all God's powers for us:  but more than that, watchfulness devotes our works to God, -- prayer devotes ourselves.  Of carnal believers Hudson Taylor, than whom none did a vaster work for Christ in the nineteenth century, and few I imgine walked closer to God, says: "They have forgotten the warning of our Lord in Luke 21:34-36, and hence are not accounted worthy to escape: they have not 'counted all things but loss,' and hence do not attain unto that resurrection, which Paul felt he might miss.  We wish to place on record our solemn conviction that not all who are Christians will attain to that resurrection, or thus meet the Lord in the air."  How much safer to strive than to assume!

Thus the cry of urgency should now ring through the whole Church of God.  Why? 
(1)  Because "if my faith is wrong, I am bound to change it: if my faith is right, I am bound to propagate it" (Dr. Whately).  To withhold the warning is to rob the Church of the very truth which is to deliver from the peril.
(2) Because no more powerful lever can be imagined for overturning our natural sluggishness.  Facts are more moving than a whole library of exhortation.  For the coming judgment of believers is a revelation levelled specifically at the flesh in the believer, and therefore can never be popular: the very bitterness with which it is assailed is an extrordinarily subtle and convincing proof of its truth.  Caleb and Joshua witnessed to the approaching Kingdom, and to the necessity for obedience as well as faith to enter it, at the peril of their lives (Numbers 14:10)  and the Lord fortells that the servant who disqualifies for reward is also the servant whose intolerance starts persecution (Matt. 24:49).  It is little wonder if those who belittle responsibility, themselves fail to achieve it. 
(3) Because the peril, however imminent, has not yet fallen. "Lukewarm Laodiceans can be roused before it is too late: Christ is standing at the door." (G.H. Pember)  Fulfillment of its conditions involves a golden certaintyof attaining the Kingdom.  "Perilous times are upon us: may it be mine to watch and pray always that I may be counted worthy to escape all these things that are coming to pass, and to stand before the Son of Man!" (John Wilkinson). 
"WHAT I SAY UNTO YOU I SAY UNTO ALL, WATCH" (Jesus Christ)[Mark 13:37]
 
 

The Day of Justice closes with the final judgment.  The Kingdom is over (1 Cor. 15:24)
The old heavens and earth have fled away: in all God's universe no object remains save one great, glittering White Throne, before which the dead, both small and great, stand. 
"And books were opened: and another book was opened, which is the book of life: and the dead were judged"  (Rev. 20:12)  Books of works- one book of names:  books of works, that all condemnation may be exactly adjusted to guilt;  a book of names, for the saved have nothingin the Book of LIfe but a name.  Works, whether before or after faith, disappear, it is the Lamb's Book, and the names, enrolled from before the foundtion of the world, as blood-washed at Calvary, are set there by sovereign, electing Grace;  and thus the merits on which we stand for eternity are solely the merits of Christ.  Therefore all believers of the Patriarchal, Legal, and Christian dispensations reign in the Eternal Kingdom. 

"And if any was not found written in the book of life, he was cast into the lake of fire." 

Calvary is the measure of God's love to the world;  Hell is the measure of His love to Christ:  for God so loved the world as to give up His Son to Calvary;  and He so loves His Son that whosoever rejects Him must be given up to Hell. 

All reformative chastisement now ceases:  punishment purges no more, and becomes punitive for ever.  But the saved are saved with an astounding salvation.  "There shall be no curse any more" (Rev. 22:3) - eternal sinlessness:"and the Throne shall be therein" - eternal communion: "and His servants shall serve Him" - eternal service: "and they shall see His face" - eternal joy:  "and His name shall be on their foreheads" - eternal security: "and there shall be night no more" - eternal energy:  "and the Lord God shall give them light" - eternal knowledge: "AND THEY" - all the risen, of all dispensations- "SHALL REIGN FOR EVER AND EVER"- eternal glory.