אליגוריות החוקים, ספר ג מ״וAllegorical Interpretation of Genesis, Book III 46

א׳
1[133] But he shall bring out the difference more clearly by means of the following words: “The breast of the offering put on, and the shoulder of the part removed, I have taken at the hands of the children of Israel from the sacrifices of your salvation, and have given to Aaron and his sons” (Lev. 7:34).
ב׳
2[134] You see that these are not capable of taking the breast by itself, but must take it with the shoulder, whereas Moses takes it without the shoulder. Why is this? Because he, being perfect, has no small or petty aims, nor any desire to moderate his passions, but goes so far as to cut off all passions everywhere; while those others set out to wage war on the passions on an insignificant, not on a grand, scale, but seek to come to terms and arrange a truce with them, putting forward the word of pacification, that this like a charioteer may curb their excessive impetuosity.
ג׳
3[135] Furthermore the shoulder is a symbol of toil and hardship; and this is the character of him who attends to and ministers in holy things, subject to toil and discipline. But the man on whom God bestows in overflowing measure his good things in perfection is free from toil. He who acquires virtue by toil is found to come short of full achievement, as compared with Moses, who received it easily and without toil from the hands of God. For, as toiling itself falls short of the toilless achievement and is inferior to it, so does the imperfect fall short of the perfect, and that which learns of that which is self-taught. This is why Aaron takes the breast with the shoulder, but Moses without the shoulder.
ד׳
4[136] The reason why he calls it the breast of “the special offering put on” is that it is necessary that the reason should be put and set firmly on the seat of anger, as though it were a kind of charioteer keeping straight a stiff-necked and restive horse. But when he comes to the shoulder he speaks of it not as in the case of the breast, as belonging to “the offering put on,” but as belonging to “that which was removed.” The reason he does so is this. It is necessary that the soul should not ascribe to itself its toil for virtue, but that it should take it away from itself and refer it to God, confessing that not its own strength or power acquired nobility, but He who freely bestowed also the love of it.
ה׳
5[137] Neither breast nor shoulder is taken except from the sacrifice of salvation. That is fitting. For only then does the soul begin to be saved, when the seat of anger has received reason as its charioteer, and toil has come to create in it, not self-satisfaction, but a readiness to yield the honour to God, the Bestower of the boon.