We believe it for one very simple reason. The Holy Spirit, the God who cannot lie, explicitl said that this will be done.
18 And He said to me, "Son of man, thus says the Lord GOD: 'These are the ordinances for the altar on the day when it is made, for sacrificing burnt offerings on it, and for sprinkling blood on it. 19 You shall give a young bull for a sin offering to the priests, the Levites, who are of the seed of Zadok, who approach Me to minister to Me,' says the Lord GOD. 20 You shall take some of its blood and put it on the four horns of the altar, on the four corners of the ledge, and on the rim around it; thus you shall cleanse it and make atonement for it. 21 Then you shall also take the bull of the sin offering, and burn it in the appointed place of the temple, outside the sanctuary. 22 On the second day you shall offer a kid of the goats without blemish for a sin offering; and they shall cleanse the altar, as they cleansed it with the bull. 23 When you have finished cleansing it, you shall offer a young bull without blemish, and a ram from the flock without blemish. 24 When you offer them before the LORD, the priests shall throw salt on them, and they will offer them up as a burnt offering to the LORD. 25 Every day for seven days you shall prepare a goat for a sin offering; they shall also prepare a young bull and a ram from the flock, both without blemish. 26 Seven days they shall make atonement for the altar and purify it, and so consecrate it. 27 When these days are over it shall be, on the eighth day and thereafter, that the priests shall offer your burnt offerings and your peace offerings on the altar; and I will accept you,' says the Lord GOD." Ezekiel 43:18-27
Again, it says,
15 "But the priests, the Levites, the sons of Zadok, who kept charge of My sanctuary when the children of Israel went astray from Me, they shall come near Me to minister to Me; and they shall stand before Me to offer to Me the fat and the blood," says the Lord GOD. 16 They shall enter My sanctuary, and they shall come near My table to minister to Me, and they shall keep My charge. 17 And it shall be, whenever they enter the gates of the inner court, that they shall put on linen garments; no wool shall come upon them while they minister within the gates of the inner court or within the house. 18 They shall have linen turbans on their heads and linen trousers on their bodies; they shall not clothe themselves with anything that causes sweat. 19 When they go out to the outer court, to the outer court to the people, they shall take off their garments in which they have ministered, leave them in the holy chambers, and put on other garments; and in their holy garments they shall not sanctify the people. 20 They shall neither shave their heads nor let their hair grow long; but they shall keep their hair well trimmed. 21 No priest shall drink wine when he enters the inner court. 22 They shall not take as wife a widow or a divorced woman, but take virgins of the descendants of the house of Israel, or widows of priests. 23 And they shall teach My people the difference between the holy and the unholy, and cause them to discern between the unclean and the clean. 24 In controversy they shall stand as judges, and judge it according to My judgments. They shall keep My laws and My statutes in all My appointed meetings, and they shall hallow My Sabbaths. 25 They shall not defile themselves by coming near a dead person. Only for father or mother, for son or daughter, for brother or unmarried sister may they defile themselves. 26 After he is cleansed, they shall count seven days for him. 27 And on the day that he goes to the sanctuary to minister in the sanctuary, he must offer his sin offering in the inner court," says the Lord GOD. 28 "It shall be, in regard to their inheritance, that I am their inheritance. You shall give them no possession in Israel, for I am their possession. 29 They shall eat the grain offering, the sin offering, and the trespass offering; every dedicated thing in Israel shall be theirs. 30 The best of all firstfruits of any kind, and every sacrifice of any kind from all your sacrifices, shall be the priest's; also you shall give to the priest the first of your ground meal, to cause a blessing to rest on your house. 31 The priests shall not eat anything, bird or beast, that died naturally or was torn by wild beasts. Ezekiel 44:15-31
The explicit words of scripture are too strong a bind to be broken by any and all the reasonings of mere men.
Here the Holy Spirit explicitly says that animal sacrifices will be offered in that day. When people reason that this is impossible, they are forgetting that the God that changed the rules when He first gave the law through Moses, and who changed them again at the cross, has a perfect right to change them again, any time He wants to do it. And here, he has explicitly stated that these will be His rules at that time.
And the very few of us that have actually studies these sacrifices, have found that this order of worship is not only different from what we are told to do at this time, but that are also different from the laws given through Moses. This is most certainly NOT a return to the law of Moses, but a new law, one that takes into account the new covenant, but does the worship in a different way.
I say that the new covenant is here taken into account, because Jeremiah 3:16 explicitly says that there will no longer be an "ark of the covenant." That was the symbol of the old covenant, and it will be gone.