A Commentary, Critical, Practical, and Explanatory on the Old and New Testaments, by Robert Jamieson, A.R. Fausset and David Brown  at sacred-texts.com
lev 21:1OF THE PRIESTS' MOURNING. (Lev. 21:1-24)
There shall none be defiled for the dead among his people--The obvious design of the regulations contained in this chapter was to keep inviolate the purity and dignity of the sacred office. Contact with a corpse, or even contiguity to the place where it lay, entailing ceremonial defilement (Num 19:14), all mourners were debarred from the tabernacle for a week; and as the exclusion of a priest during that period would have been attended with great inconvenience, the whole order were enjoined to abstain from all approaches to the dead, except at the funerals of relatives, to whom affection or necessity might call them to perform the last offices. Those exceptional cases, which are specified, were strictly confined to the members of their own family, within the nearest degrees of kindred.
lev 21:4But he shall not defile himself--"for any other," as the sense may be fully expressed. "The priest, in discharging his sacred functions, might well be regarded as a chief man among his people, and by these defilements might be said to profane himself" [BISHOP PATRICK]. The word rendered "chief man" signifies also "a husband"; and the sense according to others is, "But he being a husband, shall not defile himself by the obsequies of a wife" (Eze 44:25).
lev 21:5They shall not make baldness upon their heads . . . nor . . . cuttings in their flesh--The superstitious marks of sorrow, as well as the violent excesses in which the heathen indulged at the death of their friends, were forbidden by a general law to the Hebrew people (Lev 19:28). But the priests were to be laid under a special injunction, not only that they might exhibit examples of piety in the moderation of their grief, but also by the restraint of their passions, be the better qualified to administer the consolations of religion to others, and show, by their faith in a blessed resurrection, the reasons for sorrowing not as those who have no hope.
lev 21:7They shall not take a wife that is a whore, or profane--Private individuals might form several connections, which were forbidden as inexpedient or improper in priests. The respectability of their office, and the honor of religion, required unblemished sanctity in their families as well as themselves, and departures from it in their case were visited with severer punishment than in that of others.
lev 21:10he that is the high priest among his brethren . . . shall not uncover his head, nor rend his clothes--The indulgence in the excepted cases of family bereavement, mentioned above [Lev 21:2-3], which was granted to the common priests, was denied to him; for his absence from the sanctuary for the removal of any contracted defilement could not have been dispensed with, neither could he have acted as intercessor for the people, unless ceremonially clean. Moreover, the high dignity of his office demanded a corresponding superiority in personal holiness, and stringent rules were prescribed for the purpose of upholding the suitable dignity of his station and family. The same rules are extended to the families of Christian ministers (Ti1 3:2; Tit 1:6).
lev 21:16Whosoever he be . . . hath any blemish, let him not approach to offer the bread of his God--As visible things exert a strong influence on the minds of men, any physical infirmity or malformation of body in the ministers of religion, which disturbs the associations or excites ridicule, tends to detract from the weight and authority of the sacred office. Priests laboring under any personal defect were not allowed to officiate in the public service; they might be employed in some inferior duties about the sanctuary but could not perform any sacred office. In all these regulations for preserving the unsullied purity of the sacred character and office, there was a typical reference to the priesthood of Christ (Heb 7:26).