Numbers 19:3 - Wesley's Explanatory Notes

Eleazar — Who was the second priest, and in some cases, the deputy of the high — priest. To him, not to Aaron, because this service made him unclean for a season, and consequently unfit for holy ministrations, whereas the high — priest was, as far as possibly he could, to be preserved from all sorts of defilement, fit for his high and holy work. Without the camp — Partly because it was reputed an unclean and accursed thing, being laden with the sins of all the people; and partly to signify that Christ should suffer without the camp, in the place where malefactors suffered.