In a sense, the kohen acts as the violator’s attorney. He offers a plea bargain on his client’s behalf. In return for a sincere resolution not to repeat the offence and the disgorgement of part of the ill-gotten gains on the altar, the Judge will grant atonement. The kohen must be a respectable representative in order to successfully represent his client. He must be sober and well dressed and his hair must be trimmed.
The two sons of Aaron, Nadav and Avihu, who, according to some commentators, ventured past the outer altar in a state of intoxication, paid for it with their lives. Indeed, a kohen who enters the Sanctuary to perform a priestly service while intoxicated is liable to death at the hand of God and the service he performed is ineffective.
Intoxication for this purpose means that the kohen has drunk at least a revi’it (between 3.3 and 4.42 fluid ounces) of wine not less than forty days old in one shot. Although a kohen may not enter the Temple under the influence of any alcoholic beverage, the consequences of entering the Temple under the influence of non-wine alcoholic beverage is less severe. The kohen will incur the punishment of malkot, lashes, but the priestly service performed under the influence will still be effective.
The kohanim were divided into twenty four mishmarot, service units. Each mishmar was sub-divided into batei avot, family units numbering one hundred sixty eight in all. Each family unit of kohanim performed the priestly service in the Temple at least two days each year. During these two days, the kohen of the family unit up for service was not permitted to drink any alcoholic beverage, neither by day nor by night and was not allowed to drink wine the entire week.
According to one opinion in the Talmud, since kohanim today do not know what mishmar or beit av they belong to, they can never drink wine because if the Messiah were to arrive the day they drank and that day happened to be their day of service, they would be unable to serve. However, in view of the fact that the Messiah is taking longer than anticipated to arrive, the halacha is not in accordance with this opinion and a kohen today may drink wine.
A kohen may not venture past the outer altar if he has not had a haircut for the last thirty days. The kohen gadol may not enter the Temple unless his hair is cut every seven days.
Even though the kohen changed out of his secular clothes into his bigdei kehunah, the priestly garments, before performing the service, the secular clothes he wore and out of which he changed upon arrival at the Temple had to be freshly laundered. A kohen who did not have his hair cut within the prior thirty days or whose garments were torn was not allowed to enter the Temple. If a kohen performed the priestly service in such a state, he was subject to the punishment of karet even though the priestly service was effective.
A kohen whose close relative had died but was not yet buried was not allowed to continue with the priestly service; he was obliged to leave the Temple to attend to the deceased. The kohen gadol, however, was obliged to continue with the priestly service as did Aaron upon learning of the death of his two sons.
The only person allowed to enter the kodesh kodashim, the Holy of Holies, was the kohen gadol, who was permitted to enter four times in order to perform the Yom Kippur service. If he entered a fifth time on Yom Kippur, or at any other time, he too risked the punishment of karet.
The only person ever granted unrestricted access to the Holy of Holies was Moses, to whom God spoke from between the wings of the keruvim, the cherubs, on the Holy Ark.