Rambam's view that sacrifices were commanded to wean the Jews from idolatry

 Contrary to the mistaken claim Rambam based himself not on Vayikra (17:7) but on rational argument

Rambam (Moreh haNevuchim 3:30) On examining these old and foolish doctrines we find that it was most generally believed by the people that by the worship of stars the earth will become inhabited, and the ground fertilized. The wise, pious, and sin-fearing men among them reproved the people and taught them that agriculture, on which the preservation of mankind depended, would become perfect and satisfy man's wishes, when he worshiped the sun and the stars. If man provoked these beings by his rebelliousness, the towns would become empty and waste. In the above-named books it is stated that Mars was angry with lands, that form now deserts and wastes, and in consequence of that anger they were deprived of water and trees, and have become the habitation of demons. Tillers of the ground and husbandmen are praised in those books, because they are engaged with the cultivation of the land in accordance with the will and desire of the stars. The idolaters also held cattle in esteem on account of their use in agriculture, and went even so far as to say, that it is not allowed to slay them, because they combine in themselves strength and willingness to do the work of man in tilling the ground. The oxen, notwithstanding their great strength, do this, and submit to man, because it is the will of God that they should be employed in agriculture. When these views became generally known, idolatry was connected with agriculture, because the latter is indispensable for the maintenance of man, and of most animals. The idolatrous priests then preached to the people who met in the temples, and taught them that by certain religious acts, rain would come down, the trees of the field would yield their fruit, and the land would be fertile and inhabited. See what is said in the Nabatean Agriculture in the chapter on vineyards. The following words of the Sabeans are quoted there: "All ancient wise men advised, and prophets likewise commanded and enjoined to play before the images on certain instruments during the festivals. They also said--and what they said is true--that the deities are pleased with it, and reward those who do it. They promise, indeed, very great reward for these things; e.g., length of life, protection from illness, exemption from great bodily deformities, plenty of the produce of the earth, and of the fruits of the trees." These are the words of the Sabeans. When these ideas spread, and were considered as true, God, in His great mercy for us, intended to remove this error from our minds, and to protect our bodies from trouble; and therefore desired us to discontinue the practice of these useless actions. He gave us His Law through Moses, our teacher, who told us in the name of God, that the worship of stars and other corporeal beings would effect that rain would cease, the land be waste, and would not produce anything, and the fruit of the trees would wither; calamities would befall the people, their bodies would be deformed, and life would be shortened. These are the contents of "the words of the covenant which God made" (Deut. 28:6-9). It is frequently expressed in all parts of Scripture, that the worship of the stars would be followed by absence of rain, devastation of the land, bad times, diseases, and shortness of life. But abandonment of that worship, and the return to the service of God, would be the cause of the presence of rain, fertility of the ground, good times, health and length of life. Thus Scripture teaches, in order that man should abandon idolatry, the reverse of that which idolatrous priests preached to the people, for, as has been shown by us, the principal object of the Law is to remove this doctrine, and to destroy its traces.

Rambam (Moreh haNevuchim 3:32) Many precepts in our Law are the result of a similar course adopted by the same Supreme Being. It is, namely, impossible to go suddenly from one extreme to the other: it is therefore according to the nature of man impossible for him suddenly to discontinue everything to which he has been accustomed. Now God sent Moses to make the Israelites a kingdom of priests and a holy nation (Exod. 19:6) by means of the knowledge of God. Comp. "Unto thee it was showed that thou mightest know that the Lord is God (Deut. 4:35); "Know therefore this day, and consider it in thine heart, that the Lord is God" (ibid. 5:39). The Israelites were commanded to devote themselves to His service; comp. "and to serve him with all your heart" (ibid. 11:13); "and you shall serve the Lord your God" (Exod. 23:25); "and ye shall serve him" (Deut. 13:5). 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. 25:8); to have the altar erected to His name; comp. "An altar of earth thou shalt make unto me" (ibid. 20:21); to offer the sacrifices to Him; comp. "If any man of you bring an offering unto the Lord" (Lev. 1:2), 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. 22:19); "For thou shalt bow down to no other God" (ibid. 34:14). He selected priests for the service in the temple; comp. "And they shall minister unto me in the priest's office" (ibid. 28:41). 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. I know that you will at first thought reject this idea and find it strange; you will put the following question to me in your heart: How can we suppose that Divine commandments, prohibitions, and important acts, which are fully explained, and for which certain seasons are fixed, should not have been commanded for their own sake, but only for the sake of some other thing: as if they were only the means which He employed for His primary object? What prevented Him from making His primary object a direct commandment to us, and to give us the capacity of obeying it? Those precepts which in your opinion are only the means and not the object would then have been unnecessary. Hear my answer, which win cure your heart of this disease and will show you the truth of that which I have pointed out to you. There occurs in the Law a passage which contains exactly the same idea; it is the following: "God led them not through the way of the land of the Philistines, although that was near; for God said, Lest peradventure the people repent when they see war, and they return to Egypt; but God led the people about, through the way of the wilderness of the Red Sea," etc. (Exod. 13:17). Here God led the people about, away from the direct road which He originally intended, because He feared they might meet on that way with hardships too great for their ordinary strength; He took them by another road in order to obtain thereby His original object. In the same manner God refrained from prescribing what the people by their natural disposition would be incapable of obeying, and gave the above-mentioned commandments as a means of securing His chief object, viz., to spread a knowledge of Him among the people, and to cause them to reject idolatry. It is contrary to man's nature that he should suddenly abandon all the different kinds of Divine service and the different customs in which he has been brought up, and which have been so general, that they were considered as a matter of course; it would be just as if a person trained to work as a slave with mortar and bricks, or similar things, should interrupt his work, clean his hands, and at once fight with real giants. It was the result of God's wisdom that the Israelites were led about in the wilderness till they acquired courage. For it is a well-known fact that travelling in the wilderness, and privation of bodily enjoyments, such as bathing, produce courage, whilst the reverse is the source of faint-heartedness: besides, another generation rose during the wanderings that had not been accustomed to degradation and slavery. All the travelling in the wilderness was regulated by Divine commands through Moses; comp. "At the commandment of the Lord they rested, and at the commandment of the Lord they journeyed; they kept the charge of the Lord and the commandment of the Lord by the hand of Moses" (Num. 9:23). In the same way the portion of the Law under discussion is the result of divine wisdom, according to which people are allowed to continue the kind of worship to which they have been accustomed, in order that they might acquire the true faith, which is the chief object of God's commandments. You ask, What could have prevented God from commanding us directly, that which is the chief object, and from giving us the capacity of obeying it? This would lead to a second question, What prevented God from leading the Israelites through the way of the land of the Philistines, and endowing them with strength for fighting? The leading about by a pillar of cloud by day and a pillar of fire by night would then not have been necessary. A third question would then be asked in reference to the good promised as reward for the keeping of the commandments, and the evil foretold as a punishment for sins. It is the following question: As it is the chief object and purpose of God that we should believe in the Law, and act according to that which is written therein, why has He not given us the capacity of continually believing in it, and following its guidance, instead of holding out to us reward for obedience, and punishment for disobedience, or of actually giving all the predicted reward and punishment? For [the promises and the threats] are but the means of leading to this chief object. What prevented Him from giving us, as part of our nature, the will to do that which He desires us to do, and to abandon the kind of worship which He rejects? There is one general answer to these three questions, and to all questions of the same character: it is this: Although in every one of the signs related in Scripture the natural property of some individual being is changed, the nature of man is never changed by God by way of miracle. It is in accordance with this important principle that God said, "O that there were such an heart in them, that they would fear me," etc. (Deut. 5:26). It is also for this reason that He distinctly stated the commandments and the prohibitions, the reward and the punishment. This principle as regards miracles has been frequently explained by us in our works: I do not say this because I believe that it is difficult for God to change the nature of every individual person; on the contrary, it is possible, and it is in His power, according to the principles taught in Scripture; but it has never been His will to do it, and it never will be. If it were part of His will to change at His desire the nature of any person, the mission of prophets and the giving of the Law would have been altogether superfluous.