Q. I've listened to your commentary on Rom. 11:25-36—The Salvation of Israel, and it's a very thorough study. I am trying to put the pieces of the Millennial Kingdom together and I'm having a problem digesting the fact that there will be sacrifices reinstated. This just doesn't seem to line up with New Covenant teaching.
Why would God want sacrifices made again when Jesus, His only-begotten Son, was the accepted sacrifice? This seems to be a direct insult to Christ, as if to say: "Your sacrifice wasn't sufficient."
Also, the reinstating of sacrifices would be going back to Judaism. And we know that Judaism and the law were the shadow of Christ, so it's as if worship in the Millennial Kingdom will be: "Worshipping the shadow instead of the reality."
Also, where is the Church going to be during this time, in Heaven or on the earth? At the resurrection we will be given a glorified body, I can hardly see us living and reigning in a carnal world after such an event.
Satan will be bound during this time and at the end he will be loosed to go about and deceive the nations into making war against the "Beloved City" (Rev. 20:9). Where do all of these nations come from if there's nothing but a Jewish remnant that enters into the Kingdom after Christ returns?
These are but a few of the questions that I have concerning the Millennial Kingdom. Your answers to these questions will be appreciated, so I look forward to hearing back from you.
Q. Why would God want sacrifices made again when Jesus, His only-begotten Son, was the accepted sacrifice? This seems to be a direct insult to Christ, as if to say: "Your sacrifice wasn't sufficient."
A. Ask yourself this question: if Jesus was the "accepted sacrifice" (and I agree that He was), then what was the purpose of the sacrifices in the OT? Were they purely to point to Him? Not according to the OT—where they are said to be atoning. They served a purpose which differed from the sacrifice of Jesus. The problem here is the assumption that the work of Jesus somehow "added to" or "completed" what animal sacrifices were for in the Old Testament. But this is not the case. In the same way that animal sacrifices in the OT did not contribute to (or take away from) the work of Christ, so too animal sacrifices in the Millennium. Animal sacrifices in the OT and in the millennium do not pertain to salvation.
Also: where do we get this "troublesome" notion of future animal sacrifices? From the plain reading of Ezekiel's prophecy. Remember that the original recipients of Ezekiel's prophecy had no New Testament—nor would it be available for hundreds of years. How would they have understood the text at face value? Passages in Ezekiel make it plain that atoning sacrifices will be a part of the Millennium. There is simply no other viable way of explaining these passages (Eze. 43:20,26; 45:15,17,20). Spiritualizing many chapters of Ezekiel provides no adequate solution. Also notice that the details of the sacrificial system (and Temple) in Ezekiel 40ff. do not match any other temple of history that we know of.
It will be distinguished from the tribulation temple as the restoration temple by the return of the Shekinah Glory of God (Eze. 43:27; cf. Eze. 10:4,Eze. 10:18-19; Eze. 11:22-23) and by Gentile worship (Isa. 60:6; Zep. 3:10; Zec. 2:11; Zec. 8:22; Zec. 14:16-19). These traits also distinguish the millennial temple from any previous historical temple (the first temple lacked Gentile worshipers; the second temple lacked the Shekinah). In addition, the literal dimensions and architectural and ritual descriptions of the millennial temple are distinctly unique. 
While there are many similarities with the sacrifices of the Mosaic Law, as there are between the sacrifices of Noah and Moses, the differences show they are not the same. It was these very differences that kept the rabbis from accepting Ezekiel into the Hebrew Canon for some time. These differences include the following. In the consecration of the altar (Mosaic: Ex. 29:1-37; Millennial: Eze. 43:18-27) there are the following differences: the Mosaic anointed the altar while the Ezekiel had no anointing; the Mosaic offered a bullock for a sin offering for all seven days while the Ezekiel offered a bullock on the first day only; the Mosaic offered no goat while the Ezekiel offers goats for the last six days; the Mosaic applied blood on the horns of the altar only while the Ezekiel applies blood on the horns, the corners, and upon the lower molding round about; for the burnt offering, the Mosaic offered a ram every day while the Ezekiel offers both a bullock and a ram every day; the Mosaic offered a ram for the consecration of the priesthood but Ezekiel has no ram for the consecration of the priesthood, only for the altar; the Mosaic had the Ark of the Covenant but the Millennial Temple will not have the Ark of the Covenant (Jer. 3:16); under the Mosaic Law, only the High Priest could enter the Holy of Holies but in Eze. 44:15-16, all priests will be able to enter; the rules of marriage found in Eze. 44:22 were applicable to only the High Priest under the Mosaic Law but in Ezekiel, they will be applicable to all priests; under the Mosaic Law, the first of Nisan was not a special holy day but will be under the Ezekiel system (Eze. 45:18); the procedure described in Eze. 45:19 differs from the Mosaic in two ways: in the animal chosen, the Mosaic had a male goat while the Ezekiel has a bullock, and in the way the animal was disposed of, the Mosaic disposed of the animal outside the camp, while the Ezekiel is inside the camp; concerning the Passover (Eze. 45:21-24), in the Mosaic, the Passover was a family affair with the head of the household performing the ritual while in the Ezekiel the Prince will perform the ritual on behalf of the nation; in the Mosaic, the Passover was a one day festival while in the Ezekiel it will last for seven days; the Mosaic offered an unblemished lamb while the Ezekiel offers a bullock; there is also a difference in the number of sacrifices offered between the Mosaic (Nu. 28:16-24) and the Ezekiel; there is also a difference in the measures of the meal offering between the Mosaic and the Ezekiel; concerning the Feast of Tabernacles (Eze. 45:25) there is a difference in the quantity of the offerings (Nu. 29:12-34) and the Ezekiel does not have the added eighth day that the Mosaic had (Nu. 29:35-38); as for the Sabbath offerings (Eze. 46:4-5), the Ezekiel requires six lambs and a ram which is more than the Mosaic (Nu. 28:9) which required only two lambs and a ram and the same will be true with the meal offering; concerning the New Moon offerings (Eze. 46:6-7), the Mosaic required two bulls, one ram, and seven lambs while the Ezekiel will require one bullock, six lambs, and one ram; there is also a difference in the daily offering (Eze. 46:13-15) since the Mosaic (Ex. 29:38-42; Nu. 28:3-4) required two lambs each day both morning and evening while the Ezekiel will require one lamb each morning and none in the evening; there is also a difference in the daily meal offering (Ex. 29:40; Nu. 28:5); in the Mosaic Law, the observance of the Feast of Tabernacles was mandatory for Jews only while under Kingdom Law it will be mandatory for both Jews and Gentiles (Zec. 14:16-21); under the Law of Moses, only Jews could be priests but under Kingdom Law, Gentiles will also serve as priests (Isa. 66:18-21). All these differences show that this is not a return to the Law of Moses but it is a new system under Kingdom Law and so it does not violate what the New Testament teaches concerning the termination of the Law with Messiah's death. 
Further evidence that the millennial temple and law differ from the Mosaic law is found in that one of the issues before the council of Jamnia was "...to discuss how to resolve interpretive problems in the Bible. The problems included Ezekiel's contradiction of Mosaic law in his vision of the reconstituted Temple (Ezekiel 40-48),..." 
There is also the matter of having a (kingly) throne in the (priestly) millennial temple (Eze. 43:7)—a clear indication that the One who occupies the throne is simultaneously both a king and priest, ala Melchizedek (Gen. 14:18) and as predicted by Zechariah 6:11-13. This is completely different than any previous temple. The HCSB provides a superior translation of the underlying Hebrew on this point:
Take silver and gold, make crowns and place them on the head of Joshua son of Jehozadak, the high priest. You are to tell him: This is what the LORD of Hosts says: Here is a man whose name is Branch; He will branch out from His place and build the LORD's temple. Yes, He will build the LORD's temple; He will be clothed in splendor and will sit on His throne and rule. There will also be a priest on His throne, and there will be peaceful counsel between the two of them. 
Q. The reinstating of sacrifices would be going back to Judaism. And we know that Judaism and the law were the shadow of Christ, so it's as if worship in the Millennial Kingdom will be: "Worshipping the shadow instead of the reality."
I don't see how fulfilling God's requirements for unglorified sinful flesh to be in his glorious presence is "worshipping a shadow." It is simply following the instructions He Himself gives in Ezekiel concerning that Temple. Your statement assumes that sacrifices in the OT were solely to point to Jesus and had no other purpose. This is not so: they were atoning and had to do with allowing sinful flesh to approach a Holy God. They did not save nor contribute in any way to the completely independent work of Christ. In the same way, Millennial sacrifices have a purpose (when Jesus reigns as God personally amidst people who have not been glorified and remain in sinful human flesh).
The situation which the Church presently enjoys—where the Holy Spirit can take up residence permanently within sinful flesh is unique to the Church age. There were preconditions related to the glorification of Jesus which had to take place before the Spirit could come in a new way on the Day of Pentecost to indwell and seal believers in our age (John 7:39; 16:7). Once these conditions were satisfied, this allowed creation of the New Testament temple wherein the Spirit of a Holy God took up permanent residence within the sinful flesh of believers (1 Cor. 3:17; 6:19; 2 Cor. 6:16; Eph. 2:21; 1 Pe. 2:5). This baptizing work of the Spirit only began with the Church age—we have no definite indication that the same relationship between a Holy God and sinful flesh will hold for saints who come to faith after the Church age—following the Rapture—and enter into the Millennium.
For more on these themes, see my presentation concerning the creation and dedication of the New Testament temple of the believer on the Day of Pentecost titled, Tongues as of Fire and the discussion of the various Temples of Scripture within the Revelation Study.
Q. Where is the Church going to be during this time, in Heaven or on the earth? At the resurrection we will be given a glorified body, I can hardly see us living and reigning in a carnal world after such an event.
This sounds like the frequently encountered belief among many Christians that the material creation is inherently inferior or bad. This view comes from Greek philosophy (gnosticism) and is not Biblical teaching (Gen. 1:31; 2:3). The Bible reveals that God will redeem the entire created realm: both the spiritual and the physical (Mat. 19:28; Rom. 8:22; Rev. 21:1). You seem to think that material blessing is carnal. Will it be carnal when we drink wine with Jesus in His Father's kingdom as He himself promised (Mat. 26:29)?
You ask where the Church is going to be? The same place all believers will be who died prior to His second coming: raised no later than the millennium to rule and reign with Christ (Rev. 3:21; Rev. 20:4). An important aspect of the Millennium is that government will be perfect because it will consist of Jesus on the throne of David and resurrected (glorified, sinless) believers. The only sin that will remain is within those who enter the kingdom in their natural bodies—believers who are alive when Christ returns—and their offspring.
Q. Satan will be bound during this time and at the end he will be loosed to go about and deceive the nations into making war against the "Beloved City." Where do all of these nations come from if there's nothing but a Jewish remnant that enters into the Kingdom after Christ returns?
Your assumption that only a Jewish remnant enters the kingdom at the return of Christ is not accurate. A careful reading of Matthew 25:31-46 (which occurs immediately following the second coming) shows there are three groups of people: (1) goats: unbelievers; (2) sheep: believers; and (3) "my brethren"—the believing Jewish remnant. The sheep and goats are from "all the nations." The sheep and "my brethren" enter the kingdom. Thus, there will be many Gentiles (sheep) as well as Jews who enter the millennium. It is the unbelieving offspring from these who rebel at the end of the thousand years (ala Psalm 2; Rev. 20:7-9).
Summary: Ezekiel's Temple is a Future Earthly Temple
The millennial kingdom is a big topic no doubt. And for many of us, when we first became believers, all we ever heard about was "heaven," "heaven," and more "heaven" but the Bible says otherwise: "heaven and earth." The material realm will exist forever and God is going to redeem it back to the state it had before the Fall. The millennial kingdom is a "half-way house" of sorts between what we experience now and the final redemption (Rev. 21:1).
For additional background on these matters, see the presentation on the millennial kingdom which is part of the Revelation Study.
May the Lord bless you as you meditate on this important topic which is often neglected by those who preach His Word.
 Mal Couch, ed., Dictionary of Premillennial Theology (Grand Rapids, MI: Kregel Publications, 1996), J. Randall Price, Temple, The Future, pp. 404-405
 Ariel Ministries Newsletter, (Tustin, CA: Ariel Ministries). Fruit from the Frucht, PART TWO THE MILLENNIAL TEMPLE - LITERAL OR ALLEGORICAL?, Fall 2012, volume 1 number 5, pp. 9-10 [http://www.ariel.org/pdf/mag-fall2012.pdf] accessed 20120102.
 Randall Price, Searching for the Original Bible (Eugene, OR: Harvest House Publishers, 2007), p. 148
 HCSB, (Zec. 6:11-13)