שמות, פרק כ״ט, פסוק כ״ו

During the inauguration of the priesthood, a special ram is brought as a peace offering. The way this animal is divided and handled carries deep legal and symbolic weight. In this unique ceremony, Moses steps into the role of the officiating priest. As a result, the breast of the ram—the portion typically reserved for the serving priest—is given to him as his portion [ביאור שטיינזלץ, בכור שור]. This is simply his designated share of the offering [אבן עזרא].

The offering is specifically associated with Aaron, without mentioning his sons. Some commentators explain that because Aaron is the central figure of the event, it is fitting to highlight his name alone [אבן עזרא, חזקוני]. Another perspective focuses on the practical laws of sacrifices. Since Aaron is the owner of this specific offering, he is not permitted to receive the priestly portion; instead, it must go to the priest performing the service, which in this case is Moses. Because Aaron does not receive this part, it naturally follows that his sons do not receive it at this time either. However, this right is preserved for future generations, when Aaron and his descendants will receive both the breast and the thigh from the peace offerings brought by the Israelites [רמב״ן, הטור הארוך, חזקוני, מלבי״ם].

The decision to give Moses the breast, rather than the right thigh that is also usually granted to the officiating priest, reveals a deeper meaning. Symbolically, the thigh represents physical strength and forward movement, which is why it is burned on the altar. The breast, however, symbolizes the heart, personal will, and spiritual thought. Moses is given the breast because the newly appointed priests owe their entire spiritual foundation to him [רש ר הירש]. Additionally, he receives this portion as a reward for protecting Aaron and for genuinely rejoicing in his heart over his brother's new role [שפתי כהן]. On a practical level, Moses does not receive the thigh because he is not wearing the official priestly garments during the service [שפתי כהן].

Giving the breast to Moses also serves as a profound mark of respect. The breast is generally considered a more significant portion than the thigh. If the thigh is burned on the altar, one might expect the more important breast to be burned as well. By directing that it be eaten by Moses instead, it teaches a powerful lesson: the consumption of the offering by the priests is equal in importance to burning it on the altar [העמק דבר].

The physical handling of the offering involves distinct motions to present it before God [בכור שור]. The process includes a waving motion, moving the offering back and forth, alongside a raising motion, lifting it up and down. These two distinct actions are mentioned together to clearly outline the different types of movements used in the sanctuary service [ברכת אשר על התורה]. Furthermore, using a variety of terms for these essential actions serves to enrich and polish the language describing the ceremony [בכור שור].