I have read one part of the Temple, but please may I ask, why will they be sacrifices for atonement of sin, if we believe that Jesus was the once and for all sacrifice.
I don't know the full answer to this, but it is clear that God will require sacrifices for expiation and offerings to honor Him.
There are several passages in the Old Testament that clearly indicate animal sacrifice will be re-instituted by the new citizens of all the holy Land. Isaiah 56:1-8, Ezekiel 20:40-41
The passage that is the most extensive, giving the greatest detail, is Ezekiel 43:18 and 46:24.
It should be noted that this is part of a greater passage dealing with the period after the Lords faithful people go to live in all of the holy Land, soon after the Land is cleared and cleansed;
before Jesus Returns.
A prophecy that plainly states how those people will build the Temple, a new Temple that will surpass all other temples previously built, even Herod’s temple that was quite large, which existed during the earthly ministry of Christ. Haggai 2:6-9
The Shekinah Glory of God will come into it. Ezekiel 43:1-4
After giving details concerning the size, 1 Kings 6:1-3, and appearance of the Temple and the Altar, the Lord then begins to give detailed instruction as to the animal sacrifices that will be offered. Ezekiel 43:18-27
In chapter 44, the Lord gives instructions as to who will be offering sacrifices to the Lord. The Lord states that all of the Levites will not be offering blood and fat to the Lord due to previous sin; it will be those from the lineage of Zadok, (verse 15). Isaiah 66:21, Revelation 5:10
Chapters 45 and 46 continue to mention that animal sacrifices will be made.
The primary objection made to the idea of animal sacrifices returning is that Christ has come and offered a perfect sacrifice for sin, and there is therefore no need to sacrifice animals for sin. However, it must be remembered that animal sacrifice never removed the sin that spiritually separates a person from the Lord.
Hebrews 10:1-4 says,
“For the Law, since it has only a shadow of the good things to come and not the very form of things, can never by the same sacrifices year by year, which they offer continually, make perfect those who draw near. Otherwise, would they not have ceased to be offered, because the worshipers, having once been cleansed, would no longer have had consciousness of sins? But in those sacrifices there is a reminder of sins year by year. For it is impossible for the blood of bulls and goats to take away sins".
It is incorrect to think that animal sacrifices took away sins in the Old Testament, and it is incorrect to think they will do so again. Animal sacrifices served as object lessons for the sinner, that sin was and is a horrible offense against God, and that the result of sin is death.
Romans 3:20 says,
“Because by the works of the Law no flesh will be justified in His sight; for through the Law comes the knowledge of sin.”
Most scholars agree that the purpose of animal sacrifice is memorial in nature. As the Lord’s Supper is a reminder of the death of Christ to the Church today, animal sacrifices will be a reminder until Jesus Returns. To those born during that time, animal sacrifices will again be an object lesson. During that future time, righteousness and holiness will prevail, but people still have earthly bodies will still have a sin nature, and there will be a need to teach about how offensive sin is to a holy and righteous God.
Animal sacrifices will serve that purpose,
"but in those sacrifices there is a reminder of sins year by year". Hebrews 10:3