The commandment to sanctify the progeny of Ahron (Hebrew "מצוות קידוש זרעו של אהרן") is a commandment based in the Hebrew Bible, and developed in rabbinical teaching that requires believers in Judaism to sanctify their priests (kohanim) in various ways. These include assisting him to abstain from any prohibitions in the Law that apply to him, and by affording him first rights in areas relating to holiness and the service of God. In the enumeration of Maimonides this is the 32nd positive commandment of the Law.
In Hebrew the commandment is literally known as the mitzvah of sanctifying the "seed of Aaron" (Hebrew מצוות קידוש זרעו של אהרן).
At the time of the Jewish Exodus from Egypt, the sacrificial activity of the Jewish nation was conducted by the firstborn of Israel. After the sin of the Golden calf, God recounted the privilege of priesthood from the firstborn and gave it to Aaron, and his sons, as an everlasting priestly covenant.
Generally, the duties of Kehuna are not restricted to sacrificial offerings alone but include various other forms of service to the nation of Israel. These forms of service include Torah instruction (Leviticus 10:10-11, Ezekiel 44:23-24) and managing tzaraath(mildew and skin disease).
Along with the commandment that God commanded Moses to confer the priesthood to Aaron came along the commandment which involves the participation of the nation of Israel in maintaining and creating a state of holiness and sanctification of their priests. Examples of this sanctification include assisting the priest in abstaining from forbidden marriages, to maintain a general state of purity, and to furnish the priest with gifts (later in rabbinical enumeration counted as twenty-four priestly gifts) to carry out his required duties.
The inauguration of Aaron and his sons to perform the holy service in the tabernacle is related in Exodus and Leviticus:And Aaron and his sons I will sanctify to serve me. And I will dwell amidst the children of Israel and I will be to them for a God. And they will know that I am the LORD their God that I took them out from the land of Egypt to dwell amongst them.
And you should sanctify him since the bread of your God he sacrifices. Holy he should be to you since holy I am the God who makes you holy.
According to the Sifsei Kohen to the Chumash since the priest or kohen is chosen by God to perform direct service to God, doing acts of sanctification to and honoring the Kohen demonstrate the sanctification of God himself in a practical setting. In a somewhat radical explanation Abraham ibn Ezra contends that the personality traits of the priest, given to him by God, are superior to those of the rest of the nation of Israel. Hence, the power to administer the priestly blessing and to be successful at prayer rests with the Kohen, thereby justifying preferential treatment from amongst the nation.
Chazal, in the attempt to quantify the meaning of "you shall make holy" explained that the requirement of the Mitzvah is to sanctify the Kohen to all matters of Kedushah;The school of Rabbi Yishmael taught; "you shall make holy" to all matters of Holiness, to open first (at addressing a gathering), to bless first (at Birchat HaMazon), and to take a fine portion first
As part of the school of Rabbi Yismael's explanation, the Mitzvah includes sanctifying the Kohen with the first slot in delivering Torah instruction from amongst other Jews who are on the/a panel of speakers. Rabbinic authorities explain that this sanctification is only applicable in the event where the Kohen is greater or equal in Torah knowledge to the other Jews present. In the event that he is not greater in Torah knowledge, this first slot is afforded the Rabbi who is superior.
The Kohen is given the honor to initiate grace after the meal provided three adult male Jews have dined together. The Shulchan Aruch HaRav points out that the Kohen is entitled to allow a non-Kohen to initiate the blessing but his permission must be explicit (Shulchan Aruch HaRav 167:19) Rashi interprets the requirement to sanctify the kohen at mealtime as affording him the initiation of making the Bracha of HaMotzi at the start of the meal.
With two honors being interpreted by the school of Rabbi Yishmael to mean spiritual forms of honor, the third is interpreted as a physical one; here, the requirement is to give the Kohen the first choice when choosing portions of equal size and value.
Every Monday, Thursday, Shabbat, Rosh Chodesh, and holy day, a pre-specified portion from the Torah is read aloud in the original Hebrew with the congregation present. On weekdays, this reading is divided into three; if a kohen is present, it is customary to honor the kohen for the first reading, a Levite for the second reading, in case no Levite is present, the same kohen who was called up for the first aliyah repeats the blessings for the second, and a member of any other tribe of Israel to the third reading.
On Shabbat, the reading is divided into seven portions, and the same rules apply for the first three readings, with a "Israelite", non-kohen and non-Levi, called up for the remaining five. If a kohen is not present, any Jew can be called up for any aliyah, but it is the custom in some congregations to then give the first Aliyah to a Levite.
Orthodox Judaism recognizes limited exceptions from the general principle that a Kohen is called first. For example, there are cases where calling a kohen first would prevent individuals celebrating special occasions from each having an aliyah. These include a groom celebrating an ufruf aliyah before a wedding, or a thirteen-year-old boy from celebrating his bar mitzvah aliyah. In large synagogues, multiple celebrations at the same time can result in a shortage of aliyot. In these situations, the Kohen is requested to forgo his birthright in respect to the needs of accommodating the occasion, Although halachically, the kohen is entitled to refuse giving up his first aliyah, the kohen will usually agree out of respect for the occasion.
The Conservative Rabbinical Assembly's Committee on Jewish Law and Standards has ruled that the practice of calling a kohen to the first aliyah represents a custom rather than a law, and thus, a Conservative rabbi is not obligated to follow it. However, Some Conservative synagogues continue to follow it.
Reform and Reconstructionist Judaism consider halakhah no longer binding, and believe the entire ancient sacrificial system to be incompatible with modern sensibilities. They also acknowledge that caste or gender-based distinctions such as having a priestly caste with distinct roles and obligations derived from heredity is morally incompatible with the principle of egalitarianism.