What does the chaining and locking of Satan in the bottomless pit for the millennial reign accomplish?

I understand your question completely I often wondered the same thing. I have reached these two possible answers

(A) The devil is released to tempt those who were resurrected in the second ressurrection (the unbelievers). So the righteous are resurrected and rule with Christ for a thousand years then after the thousands years the second resurrection begins (resurrection of the unbelievers) the devil is loosed and this group falls to ultimate temptation and after there evil plan to invade the camp of christ is thwarted by God's power, the white throne judgement takes place and the devil and all his followers get thrown into the lake of fire and the unbelievers undertake "the second death" and then the kingdom of God (New Jerusalem) descends from heaven and the New Earth will be blessed and over abundant in natural resources and all the nations of the New Earth will be blessed from New Jerusalem (the capital of the New Universe).
Revelations 20:4-6, Revelation 20:12-13, Revelations 20:14, Revelations 11:15

(B) The second answer is a speculation. After the thousand years is over and the Devil is released he goes and accomplishes tempting angels to join his rebelion by lieing and claiming that he broke out of the pit and that he cannot be contained and some angels (whom are capable of disobedience) actually believe him and fall for his deciet and begin to go against the camp of Christ and are defeated by God's power then thrown into the lake of fire never to be released.

I believe the first answer is a more palletable and acceptable answer.

Nobody has mentioned the true Olive tree; the Jews. God did not assimilate the original people of His heart into the Gentile Bride.

According to Revelation symbolism, much of which typifies The Jews, the Millenial reign will be the climax of their jealousy.

Believers are given the mandate to stir them to jealousy and a desire for the Messiah they rejected but we, the grafted in ones, accepted.

The answer rhetorician gave is outstanding. I'd like to add one more point that scripture explicitly states about the millenial reign of Christ on earth: the earth will be at rest.

Now, the implications are profound, among them rhetorician's point.

Here's another implication: all of those in the second resurrection will experience a sharp contrast (to put it mildly ;-) of a world they knew in the first life with a world that's had a millennium to operate under Christ reigning on earth with those in the first resurrection.

"The rest of the dead did not come to life until the thousand years were completed. This is the first resurrection. Blessed and holy is the one who has a part in the first resurrection; over these the second death has no power, but they will be priests of God and of Christ and will reign with Him for a thousand years" Rev 20:5-6

Next, a 'judgement' is not, only, a decision. Rather it is a period of time to come to a decision. And, that is definitely throughout many examples in scripture where God gives mankind time to repent. It is part of the judgement.

The major prophets touch some here and there on what that millenial world will be like, e.g. Isaiah chapters 65 and 66. But, more.

Consider the implications: those who get to live a period of time under Christ's reign after having lived in this world. Who is going to say, "Man, that prior age was great?" Especially in contrast to 1,000 years of Christ on earth? (e.g. Rev 2:27).

As for those who are fulfilled in this world, Jesus does address this, e.g. Lk 6:25 "Woe to you who are well fed now". Indeed. Scripture talks about how those successful by this age's standards, and feel secure or satisfied with it, are going to end up in shame.

The overwhelming majority of mankind that has experienced life in this age pretty much agree the world is a bad place. And, that includes the overwhelming majority of the successful of this age.

It is evident in scripture many will accept Christ after experiencing the contrast. But, rhetorician's point is a very good one: there are still going to be some who do not.

There is, explicitly, a first resurrection and a second resurrection of the rest of the dead. Given the totality of scripture's revelation on the matter, all those in the second resurrection are not condemned. In fact, there's another discussion on the topic God isn't even calling everyone in this age (e.g. John 6:44, "no man can come to me lest the Father draw him", and deliberate spiritual blindness/deafness imparted by God to many in this age).

Those in the second resurrection do not have a 'better resurrection' (Heb 11:35).

Also, consider the theme of birthright throughout the Bible and some correlations to first and second resurrection, e.g.

"Instead of your shame you will receive a double portion", Isa 61:7

It's not explicit, but there is definitely a notable correlation throughout scripture.

A last point about releasing Satan: it proves how futile mere mortal is against Satan. Upon being released into a world without war for 1,000 years, mere mortals are still pawns in Satan's hand to stir up war against Christ. Then, again, Christ proves how futile Satan's attempts are to thwart Him.

Apparently, Christ wants that demonstrated - again - after binding him 1,000 years. My personal thoughts are for these reasons:

• there is no struggle between ANYTHING and God. Period. Satan is not a worthy opponent to God. Yet he's fooled millinea of mankind he is just that. (Look what exalting one's self against God did for mortals. What do you think an even more accountable being is facing?)

• that should put mere mortal's hearts at rest, "be anxious for NOTHING" is God's will.

• God's revealed nature in scripture indicates He is righteously indignant of what Satan has done with His creation, ---and His Name---. It's curtains for this creature in front of all mankind and the saved.

The essence of the millennial reign is to continue and finish the teaching man was receiving back in the garden of Eden before sin interrupted. That teaching was meant to arm man with the knowledge of truth. It was this lack of truth that made man fall cheapishly for Satan's lies and trick.

The last days saint who are privileged to come to the knowledge of the totatilty of the truth of the word of God through the guidance of the Holy Spirit of truth would be at the forefront with Christ teaching the patriarchal saints and all those clouds of witnesses who began the race before us but were not fulfilled yet because their fulfillment depended on the last runners fulfillment (the first shall be the last and the last be the first). At the millennial reign, the truth of the kingdom which is a life in the last days saints will be manifested and taught for the world to see and learn for THY KINGDOM COME AND THY WILL BE DONE ON EARTH AS IT IS IN HEAVEN but as it is written, the world of sin wouldn't be able to accept the Spirit of truth even in His beauty and glory but as many that are the children of the kingdom of God would embrace the Spirit of Truth. Satan would be released again after the reign and as many who has not the Spirit of truth would still be deceived to follow him to be perpetually doomed.

This sets the stage for the final judgment and reward for every dead and living souls respectively.

Perhaps the simplest--yet most profound--reason for Satan's being chained for a thousand years is because God desires to prove to humanity once and for all that even with Satan out of the way, human beings will still reject the Lordship of Jesus Christ, thinking they are better off being masters of their own fate instead of subjects of the King of kings and Lord of lords (Revelation 17:14; 19:16).

In other words, at the end of the thousand years, no one can any longer legitimately blame only Satan for something that is deep within the heart of all of us; namely, our sin nature.

To be sure, Jesus entered time and space as the God-Man to destroy through his death and resurrection the works of the devil (1 John 3:8), but he did not enter time and space to destroy the sin nature of the creatures he created in His image. That is something each true believer needs to do of his or her volition as they put to death the works of their sinful nature (see, for example, Romans 8:13 and Colossians 3:5).

What the 10 servants of the nobleman in Jesus' parable said of their master in Luke 19 will also be on the lips of those who refuse to bow the knee to the reign and rule of Jesus on earth during the Millennium:

"'We will not have this man to reign over us'" (vv.19 and 27).

When Satan is finally loosed from his captivity, he will have little trouble, then, in rallying troops around him in his ultimately futile attempt to depose by force the King of kings and the Lord of lords, Jesus Christ. King Jesus, in turn, will have no difficulty in defeating the prince of darkness and the father of lies, as well as all those who align themselves with him and with the beast and the false prophet. After their defeat, the unholy trinity will be cast into the lake of fire forever (see Revelation 19:20; 20:10; 20:14-15).

Only then will

"'The kingdoms of this world . . . become the kingdoms of our Lord, and of his Christ; and he shall reign for ever and ever' (Revelation 11:15 KJV).