R. Gidon Rothstein (link):
Giving them some apparent (I stress the word) comfort is the view of Rambam in Moreh Nevuchim, who suggests that God instituted sacrifice because the people of the time of the Exodus were not ready for a sacrifice-free world. In weaning them from it, God restricted it to one place and only certain forms.
Only by knowing a bit of Rambam can we avoid the common error of assuming that he meant to imply that sacrifice has no other importance, and would not occur in a future Temple. First, as Prof. Twersky zt”l noted (and R. Lichtenstein has quoted approvingly), that section of the Moreh is not so much devoted to giving the reason for the mitsvot, but a reason. Rambam was trying to show that mitsvot are logical, not that he had captured the absolute reason for them (as he himself stresses in the Mishneh Torah, again as Prof. Twersky zt”l demonstrated).
If so, that Rambam’s reason no longer applies in no way implies that sacrifice itself has become irrelevant. Rambam’s having spent so much of the Mishnah Commentary and the Mishneh Torah explaining and expounding the laws of sacrifice and ritual purity—laws that did not apply in his own time, and were usually left out of halachic works of his time—should be enough of a proof of his commitment to their continuing importance.