ויאמר ה' אל משה אמור אל הכהנים, what has been written earlier so that they will understand and instruct each other in the various categories of ritual impurities and contaminations, including the difference between ritually pure domestic beasts and birds, for these are the aspects of foremost concern to the priests on a regular basis as we read in 10,10-11 ולהבדיל בין הקדש ובין החול, ובין הטמא ובין הטהור ולהורות, “and to separate the sacred from the profane, and the ritually impure, and between the ritually contaminated, and to teach these values.”

ואמרת אליהם, that the need to exercise caution in addition to these categories of the ritually pure and that which is not, also in regard to impurity conferred through contact with the dead as well as through desecrating their seed.

לנפש לא יטמא בעמיו, no one of the priestly caste must ritually defile himself through dead bodies belonging to his nation., i. e. any dead person who is not one of the seven family members for whose sake he is to ritually contaminate himself to arrange for their burial, etc.

לא יטמא בעל בעמיו להחלו, the reason why a priest is not to defile himself through contact with the dead except those of his next of kin, is that also the priest is indeed a בעל בעמיו, a distinguished, highly placed member of his people, it is his task to understand and teach these laws as we know from Maleachi 2,7 “for the lips of the priest are meant to guard knowledge, and Torah and the people will enquire concerning these from his mouth.” This makes him a person to be treated in the manner one treats a politically highly placed person, a king. Seeing he is supposed to be ever ready to serve the King of Kings, in His Temple, it is not appropriate for such a person to desecrate his status even temporarily in order to participate in the burial rites of ordinary people. According to our sages in Sanhedrin 47 the prime purpose of burying and eulogising the dead is to render honour to them. This conflicts with the honour the priests have to accord to G’d on an ongoing basis. However, the Torah exempts the priests from this restriction for burial and eulogising of near relatives from this rule. [some of the last line is my own wording, though it corresponds to the thoughts expressed by the author. Ed.]

לא יקרחו, even though I have permitted the priests to defile themselves to bury their close relatives and express mourning rites, I have not permitted them to exaggerate such displays of mourning to include the making of bald spots on their heads and to make incisions in their flesh. As our sages phrased it, “just as the previous verses dealt with the dead, so the verses in front of us deal with honour for the dead.”(Torat Kohanim 1,3)

ולא יחללו שם אלוקיהם, even though all of the aforementioned were expressions of grief over the loss of relatives, the priest is not permitted to disregard the dignity which his status as priest imposes upon him. Even though the priests, no doubt, mean to honour G’d in what they are doing, when they disregard the restrictions their status imposes upon them, they indirectly desecrate the name of the Lord.

כי קדוש הוא לאלוקיו, every member of the tribe is by definition בעל בעמיו, an especially distinguished personage among his people. If he were to marry someone guilty of or unfortunate enough to belong to the categories mentioned in this verse, the husband would no longer be entitled to the sanctity his birthright had not only entitled him to but had expected him to preserve.

ומן המקדש לא יצא. According to Rabbi Saadyah gaon, this means primarily joining the funeral cortege which requires leaving the holy precincts.

ולא יחלל את מקדש אלוקיו, so as not to desecrate the Temple of his G’d, as people would conclude that giving honour to the dead is more important than to remain within the sphere of G’d’s immediate presence, something he enjoys as the exceptional privilege of being exposed to on an ongoing basis.

כי כל איש אשר בו מום לא יקרב, to stand and perform the Temple service. The principle is familiar to us from when Esther was aghast when her uncle Mordechai appeared wearing sackcloth in the courtyard of the Royal Palace (Esther 4,2).

שבר רגל, an example of blemishes not caused by the priests’ bodies themselves.

או גבן, (eyebrow) an example of blemishes caused by the body being deficient in some of its essential moisture.