Why there will be a end-time judgment

Many look at this verse and wonder what it means for them:
Matthew 7:21-23 King James Version (KJV)
21 Not every one that saith unto me, Lord, Lord, shall enter into the kingdom of heaven; but he that doeth the will of my Father which is in heaven.
22 Many will say to me in that day, Lord, Lord, have we not prophesied in thy name? and in thy name have cast out devils? and in thy name done many wonderful works?
23 And then will I profess unto them, I never knew you: depart from me, ye that work iniquity.

Now we know that at the Second Coming, Christ would have to make a decision or rule on those that would be saved. But there are some who say they are of the "New Covenant" that it is incompatible with the doctrine of justification by grace alone, through faith alone, on the account of Christ alone.

So we must look to the scriptures, we see this:
Matthew 18:23-35 King James Version (KJV)
23 Therefore is the kingdom of heaven likened unto a certain king, which would take account of his servants.
24 And when he had begun to reckon, one was brought unto him, which owed him ten thousand talents.
25 But forasmuch as he had not to pay, his lord commanded him to be sold, and his wife, and children, and all that he had, and payment to be made.
26 The servant therefore fell down, and worshipped him, saying, Lord, have patience with me, and I will pay thee all.
27 Then the lord of that servant was moved with compassion, and loosed him, and forgave him the debt.
28 But the same servant went out, and found one of his fellowservants, which owed him an hundred pence: and he laid hands on him, and took him by the throat, saying, Pay me that thou owest.
29 And his fellowservant fell down at his feet, and besought him, saying, Have patience with me, and I will pay thee all.
30 And he would not: but went and cast him into prison, till he should pay the debt.
31 So when his fellowservants saw what was done, they were very sorry, and came and told unto their lord all that was done.
32 Then his lord, after that he had called him, said unto him, O thou wicked servant, I forgave thee all that debt, because thou desiredst me:
33 Shouldest not thou also have had compassion on thy fellowservant, even as I had pity on thee?
34 And his lord was wroth, and delivered him to the tormentors, till he should pay all that was due unto him.
35 So likewise shall my heavenly Father do also unto you, if ye from your hearts forgive not every one his brother their trespasses.

We see that like the Lords Prayer, we must forgive our debtors:
Matthew 6:12-15 King James Version (KJV)
12 And forgive us our debts, as we forgive our debtors.
13 And lead us not into temptation, but deliver us from evil: For thine is the kingdom, and the power, and the glory, for ever. Amen.
14 For if ye forgive men their trespasses, your heavenly Father will also forgive you:
15 But if ye forgive not men their trespasses, neither will your Father forgive your trespasses.

All hidden sin will be revealed:
1 Corinthians 3:13 King James Version (KJV)
13 Every man's work shall be made manifest: for the day shall declare it, because it shall be revealed by fire; and the fire shall try every man's work of what sort it is.

And God will judge all:
2 Corinthians 5:10 King James Version (KJV)
10 For we must all appear before the judgment seat of Christ; that every one may receive the things done in his body, according to that he hath done, whether it be good or bad.

Romans 14:10-12 King James Version (KJV)
10 But why dost thou judge thy brother? or why dost thou set at nought thy brother? for we shall all stand before the judgment seat of Christ.
11 For it is written, As I live, saith the Lord, every knee shall bow to me, and every tongue shall confess to God.
12 So then every one of us shall give account of himself to God.

Hebrews 10:30 King James Version (KJV)
30 For we know him that hath said, Vengeance belongeth unto me, I will recompense, saith the Lord. And again, The Lord shall judge his people.

All secret things will be brought out:
Ecclesiastes 12:13-14 King James Version (KJV)
13 Let us hear the conclusion of the whole matter: Fear God, and keep his commandments: for this is the whole duty of man.
14 For God shall bring every work into judgment, with every secret thing, whether it be good, or whether it be evil.

And the reward given:
Matthew 16:27 King James Version (KJV)
27 For the Son of man shall come in the glory of his Father with his angels; and then he shall reward every man according to his works.

Revelation 22:12 King James Version (KJV)
12 And, behold, I come quickly; and my reward is with me, to give every man according as his work shall be.

There is a judgment going on in heaven right now and if, when Jesus comes, His reward is with Him, it stands to reason that at some point before the second coming, those who are alive on earth will have to be judged as well. All Christians believe there is a close of probation, even though they don’t use the phrase, a point when people can no longer switch sides. So there will be a cut off period at the end where the judgment will close and Christ will return and take His people, who have truly accepted Christ and His righteousness and consequently whose works show the fruits of the Spirit, to heaven as He promised.

John 14:1-3 King James Version (KJV)
1 Let not your heart be troubled: ye believe in God, believe also in me.
2 In my Father's house are many mansions: if it were not so, I would have told you. I go to prepare a place for you.
3 And if I go and prepare a place for you, I will come again, and receive you unto myself; that where I am, there ye may be also.

 

Very true, and "by their fruits ye shall know them"...
Matthew 7:20-22 King James Version (KJV)
20 Wherefore by their fruits ye shall know them.
21 Not every one that saith unto me, Lord, Lord, shall enter into the kingdom of heaven; but he that doeth the will of my Father which is in heaven.