דברים, פרק ט״ו, פסוק כ׳

Bringing the firstborn animals of the flock to be eaten in Jerusalem serves as a powerful recognition of God’s continuous care over agricultural and economic cycles. It is a profound statement of gratitude for the renewing blessings of the herd. Although the animal is brought to the altar, where its blood and fats are offered, the meat itself is given to the priest. By eating this meat with his family, the priest is essentially receiving food directly from God's table [רש״י, אבן עזרא, רבנו בחיי, רש ר הירש, בכור שור, ביאור יש״ר].

Because this meal takes place in God's chosen city, it carries a unique holiness. Even though the firstborn offering does not atone for sins like other sacrifices, it is far more than a standard priestly gift. It functions as a highly spiritual event, much like a person invited to dine in the presence of a ruler [העמק דבר].

The offering is tied to a strict annual schedule. However, unlike other sacrifices that must be brought at the very first holiday opportunity, the firstborn can be kept and eaten at any point during its first year of life [העמק דבר]. This one-year limit serves a practical purpose. It prevents the priest from accumulating large herds of firstborn animals over a long period, which could easily lead to the forbidden acts of shearing their wool or putting them to work [רלב״ג]. Beyond practical concerns, the yearly cycle carries deep meaning. It forces a person to pause and reflect on God’s ongoing providence, framing every single year as its own distinct unit of divine kindness [רש ר הירש].

The primary approach among commentators is that while the ideal practice is to consume the animal within its first year, the meat does not become invalid if the year passes before it is slaughtered. Furthermore, the annual timeframe hints at a unique bridge between two years. If the priest slaughters the animal on the very last day of its first year, he is permitted to eat it on that day as well as on the following day, which falls into the new year. This grants a total eating window of two days and one night [רש״י, מזרחי, תורה תמימה, משכיל לדוד]. The exact calculation of this year is precise and depends on the structure of the calendar. For instance, during a leap year, an animal born in the first month of Adar will only complete its full year in the month of Adar the following year [תורה תמימה].