A priest is forbidden to enter the Temple except at the time of the service, nor may anyone enter the holy of holies except for the high priest at the proper times during the Yom Kippur service, as it says "And he shall not come at all times into the holy place inside the curtain in front of the cover that is on the ark, and he shall not die".¹ A priest is forbidden to leave the Temple during the service, as it says "And you shall not leave the tent of meeting lest you die",² and it says regarding the high priest "And he shall not leave the Sanctuary".^3,a

A drunken priest is forbidden to enter the Temple beyond the altar; but if he does so his service is fit unless he has drunk wine, as it says "[And Ha-Shem said to Aaron: You shall not drink wine or intoxicating drinks, you or your sons, when you come into the tent of meeting] and you shall not die".⁴ Similarly, it is forbidden for anyone to rule on a nontrivial point of law when drunk, as it says "And to teach the children of Israel".^5,b

A priest whose hair has grown for 30 days or more or whose clothes are torn is also forbidden to go beyond the altar, as it says "They shall not shave their heads nor grow long hair... and no priest shall drink wine when they come into tbe inner court"⁶; and it says "You shall not let your head [hair] grow long or tear your clothes and you shall not die"⁷; and it says regarding the high priest "He shall not let his head [hair] grow long or tear his clothes".⁸ However, the service of such priests is fit.^c

A priest who has certain visible physical defects is also forbidden to go beyond the altar even if the defect is not permanent. Such a priest is also forbidden to participate in the service, and if he does so his service is unfit, as it says "[Say to Aaron: Any man of your descendants] who has a blemish shall not come near to offer his G-d's bread, for any man who has a blemish shall not come near... he may eat of his G-d's bread... but he shall not come to the curtain nor approach the altar [for he has a blemish and he shall not profane My sacred things]".^9,d

A priest who has just lost a close relative should not participate in the service, and if he does so his service is unfit. The high priest, however, can serve even on that day, as it says "[For any dead persons...] he shall not leave the sanctuary and he shall not profane his G-d's sanctuary".¹⁰ But not even the high priest can share in the eating of the sacrifices on that day, as it says "If I eat a sin-offering today will it be proper in the eyes of Ha-Shem?"¹¹ Similarly, if a person is in mourning or impure to a major degree his sacrifices cannot be offered.^e

An impure person is forbidden to serve in the Temple and if he does so his service is unfit, as it says "[Say to Aaron and to his sons:] They must abstain from the sacred things of the children of Israel lest they defile My holy Name... [any man of all your descendants who approaches the sacred things that the children of Israel sanctify to Ha-Shem with his impurity upon him, that person shall be cut off...] and they shall die if they profane it".¹² He is forbidden to do so even after he has immersed himself as long as the day has not ended, as it says "And they shall not profane the Name of their G-d",¹³ and it says "[If he has washed his flesh with water] and the sun has set he becomes pure".¹⁴ His service is unfit even if he has not yet brought a sacrifice on account of impurity, as it says "And the priest shall atone for her and she shall become pure"¹⁵ -- implying that until the atonement, purification is not complete. The communal sacrifices which must be brought at fixed times can be brought if necessary even in a state of impurity, but they are not eaten under such circumstances. The priests are commanded to wash their hands and feet before serving in the Temple and if they do not do so their service is unfit, as it says "And Aaron and his sons shall wash their hands and feet from it; [when they enter the tent of meeting] they shall wash in water and not die".^16,f

An impure person is forbidden to enter a holy place: a leper must not enter a walled city in the land of Israel; a person impure on account of a running issue must not enter the Temple mount; a non-Jew or a person impure on account of contact with a corpse must not enter the outer zone; a person who has immersed himself for impurity on that day must not enter the women's court; and a person who has not yet brought a sacrifice for impurity must not enter the westernmost part of the court -- as it says "[If there is a man among you who is not pure...] he shall go outside the camp; he shall not come inside the camp"¹⁷; and it says "And they shall not make their camp unclean [in which I dwell among them]"¹⁸; and it says "And if he does not wash [his clothes] and does not wash his flesh he shall bear his sin¹⁹; and it says "Or a person who touches any impure thing... [and he forgets it... he shall bring his guilt-offering to Ha-Shem]".²⁰ We are commanded to send all such persons out of the places that they are forbidden to enter, as it says "And they shall send out of the camp every leper and every person with a running issue and every person impure on account of a corpse"²¹; and it is forbidden to bring such impure things or persons into such places.^g

A non-priest or an uncircumcised person is forbidden to serve in the Temple and if he does so his service is unfit, as it says "And an outsider shall not come near you... and an outsider who comes near shall be killed".²² A priest who has committed idolatry or has offered sacrifices outside the Temple should not serve in the Temple, as it says "[Since they have served before their abominations]... they shall not approach Me to be My priests"²³; similarly, an apostate's sacrifices cannot be offered. The service must be performed while standing (as it says "To stand and serve"²⁴) directly on the Temple floor and must be performed with the right hand; otherwise it is unfit.^h

Sources:
1. Lev. 16:2	a. 2:2-5
2. Lev. 10:7	b. 1:1-3; see 15
3. Lev. 21:12	c. 1:8-11,14
4. Lev. 10:9	d. 6:1-2,7,12
5. Lev. 10:11	e. 2:6-8,11-12
6. Ezekiel 44:20-21	f. 4:1,4-5,10-11; 5:1-2 (compare Beis ha-Bechirah 7:21)
7. Lev. 10:6	g. 3:1-8,10,12,16; compare Beis ha-Bechirah 7:13-18
8. Lev. 21:10	h. 5:16-18; 6:8; 9:1,13-14; Maaseh ha-Korbanos 3:4
9. Lev. 21:17-18,22-23
10. Lev. 21:11-12
11. Lev. 10:19
12. Lev. 22:2-3,9
13. Lev. 21:6
14. Lev. 22:6-7
15. Lev. 12:8
16. Ex. 30:19-20
17. Deut. 23:11
18. Num. 5:3
19. Lev. 17:16
20. Lev. 5:2,6
21. Num. 5:2
22. Num. 18:4,7
23. Ezekiel 44:12-13
24. Deut. 18:5