Presence

In Book 3, Chapter 32 of the Moreh Nevuchim (Friedlander translation available from Wikisource, which will have to suffice until the copyright on Pines' version expires), Maimonides writes:

The Israelites were commanded to devote themselves to His service; comp." and to serve him with all your heart" (ibid. xi. 13):" and you shall serve the Lord your God" (Exod. xxiii. 25);" and ye shall serve him" (Dent. xiii. 5). But the custom which was in those days general among all men, and the general mode of worship in which the Israelites were brought up, consisted in sacrificing animals in those temples which contained certain images, to bow down to those images, and to burn incense before them; religious and ascetic persons were in those days the persons that were devoted to the service in the temples erected to the stars, as has been explained by us. It was in accordance with the wisdom and plan of God, as displayed in the whole Creation, that He did not command us to give up and to discontinue all these manners of service; for to obey such a commandment it would have been contrary to the nature of man, who generally cleaves to that to which he is used; it would in those days have made the same impression as a prophet would make at present if he called us to the service of God and told us in His name, that we should not pray to Him, not fast, not seek His help in time of trouble; that we should serve Him in thought, and not by any action.

For this reason God allowed these kinds of service to continue; He transferred to His service that which had formerly served as a worship of created beings, and of things imaginary and unreal, and commanded us to serve Him in the same manner; viz., to build unto Him a temple; comp." And they shall make unto me a sanctuary" (Exod. xxv. 8): to have the altar erected to His name; comp." An altar of earth thou shalt make unto me" (ibid. XX. 2 1): to offer the sacrifices to Him; comp." If any man of you bring an offering unto the Lord" (Lev. i. 2), to bow down to Him. and to burn incense before Him. He has forbidden to do any of these things to any other being; comp." He who sacrificeth unto any God, save the Lord only, he shall be utterly destroyed * (Exod. xxii. 19):" For thou shalt bow down to no other God" (ibid. xxxiv. 14). He selected priests for the service in the temple; comp." And they shall minister unto me in the priest's office" (ibid. xxviii. 41). He made it obligatory that certain gifts, called the gifts of the Levites and the priests, should be assigned to them for their maintenance while they are engaged in the service of the temple and its sacrifices.

By this Divine plan it was effected that the traces of idolatry were blotted out, and the truly great principle of our faith, the Existence and Unity of God, was firmly established; this result was thus obtained without deterring or confusing the minds of the people by the abolition of the service to which they were accustomed and which alone was familiar to them.

This famous passage is used by some as a proof that Maimonides would not require sacrifices in the third Temple. There's a few problems with this, however. First is that in Laws of Kings, Rambam states that in the Messianic era, there will be a third Temple, and that sacrifices will be offered there. While bringing a proof from the Yad to contradict the Moreh is not necessarily a valid approach, since Maimonides makes a disclaimer that he will intentionally make explicit contradictions with things he has written in his earlier works, and only those with the proper understanding will be able to discern his true opinion, nevertheless, one of Maimonides foundational tenets is that the Law of Moses will not change. As such, it would seem that, although Maimonides feels that the ideal form of worship would not be through sacrifices, since the Law of Moses was implemented in such a fashion, we are tied to that implementation.

Another issue: the logical deduction made from the above passage is that since sacrifices are not the ideal form of worship, then in a future Temple, being that we have now progressed and are accustomed to a more appropriate form of worship, the older, less-than-ideal forms would be put aside. There's just one problem with this logic: the Temple itself is listed as one of those less-than-ideal modes of worship. The question, then, is not whether or not Maimonides would require sacrifices in the third Temple, but whether or not Maimonides felt a third Temple itself would even be historical reality. Granted, in Maimonides depiction of the the Messianic era in the Yad, he leaves open the possibility of there not being a Temple, there's no getting around the fact that from a logical perspective, asking whether or not sacrifices would be extant is a invalid argument.

A final note: if you've heard rumor of the secret opinion of the Guide, of how Maimonides hid his true opinion in statements that seem to coincide with the accepted, common opinion, while in actuality he is covertly communicating an idea that is very much different from, and often at odds with, the norm, the above quoted passage provides a good example of such a "secret" opinion. Read it carefully, and you will learn Maimonides true opinion.