The haftara for Parashat Emor is a prophecy in Sefer Yechezkel (chapter 44) which foresees the service performed by the kohanim in the third Beit Ha-mikdash. Towards the beginning of the haftara (verses 17-18), the prophet emphasizes the requirement that the kohanim must don special priestly vestments while performing the Temple rituals. Thereafter, in verse 19, the prophet instructs that the kohanim must change out of these special garments before leaving the Mikdash:
And when they leave to the outer courtyard – to the outer courtyard to the nation, they shall remove the garments with which they administer [inside the Temple] and leave them there, in the holy chamber. They shall wear other garments, so that they do not sanctify the nation with their garments.
Targum Yonatan explains the final clause of this verse – "so that they do not sanctify the nation with their garments" – to mean, "they shall not mix together with the nation in their garments." As Radak and Metzudat David explain, the Targum understood this instruction as intended to ensure that a clear distinction in status be maintained between the kohanim and the rest of the people. Had the kohanim been allowed to mingle with the rest of the nation with their special priestly vestments, people might wrongly interpret this to mean that the commoners share the kohanim's unique status.
The sight of a kohen in his bigdei kehuna speaking and spending time with other Jews might mislead people into believing that there is little difference between a kohen officiating in the Mikdash and the rest of the nation. In order to underscore the unique status of the kohanim, the prophet instructed that the special priestly vestments must remain in the Temple away from the people, so that they will recognize the distinct, sacred status of the kohanim. According to this interpretation, the phrase "that they do not sanctify the nation with their garments" refers to the concern that the garments' presence among the people might give the mistaken impression of "sanctifying the nation," of elevating the masses to the same stature as the kohanim.
Rav Mendel Hirsch, in his commentary to the haftarot, explains differently:
Certainly the priestly garments have such meaning and importance that any act of the offerings done without the officiating priests being clad in them is invalid, and is as if performed by a zar, a non-priest… For, as the garments have to be the property of the community, when he is invested in it, the personality of the priest entirely disappears and he stands there as the servitor of the Sanctuary, and only so can he function as such… But that only goes for the procedures that are to be done in the name of the Sanctuary. The importance of the priests, however, goes farther. It is exhaustively condensed in two words of our sedra – "ve-hayu kodesh" (20:6) – they themselves are to be a Sanctuary. Wherever they are, outside the Temple too, not by their clerical appearance, but by their whole personality, by their whole life, in conduct and deed, by the pure noble model way in which they live it, they are to influence the people to live holy lives, and through their example – by no means through their clothes – prepare the basis, in the lives of the people, for the realization of these truths and aims which they express symbolically by the procedures which they conduct in the Temple. For the pomp of ornate pontifical garb there is no place in the realm of the Divine Torah. But rather, the hypocritical haughty assumption of superior holiness worn on the surface receives the sharpest condemnation.
According to Rav Hirsch, this phrase should be read as, "for not with their clothes do they sanctify the people." The prophet requires the kohen to remove the bigdei kehuna before leaving the Mikdash because his job as educator and role model is to be performed through his personality and conduct, rather than through external appearance. Although thebigdei kehuna serve a vital, indispensable function inside the Mikdash, as an expression of respect and reverence for the site of the Shekhina, outside the Temple it is the kohen himself, rather than his clothing, that must inspire the people. This requirement is thus part of the prophet's charge to the kohanim to lead, guide and teach by personal example, by displaying the kind of conduct and demeanor that will inspire without the artificial effect of ornate garments.