17 And Moses and Aaron took these men which are expressed by their names:
18 And they assembled all the congregation together on the first day of the second month, and they declared their pedigrees after their families, by the house of their fathers, according to the number of the names, from twenty years old and upward, by their polls.
19 As the Lord commanded Moses, so he numbered them in the wilderness of Sinai.
Moses and Aaron always appear in pairs. Aaron is the forefather of the priesthood, Moses the only interlocutor with God. While representing different traditions, the combination of the two figures reflects the interest of the authors of the book of Numbers, or the priestly class returned from exile. Aaron is the forefather of the Jewish priesthood, while Zadok will be the progenitor of the High Priests.
The community is here called qahal (i.e. community) while in other cases it is called eda‘ (i.e. assembly). There is not a substantial difference between the two terms, at least in this phase of tradition. Similarly to the case of Moses and Aaron, even these two terms that originally belonged perhaps to different environments and served to different functions, now both represent the one and large community of Jews gathered around the Temple cult, governed by the legislation of the Torah (= The Law) and having YHWH as the sole and exclusive God. This is a point of arrival and not of departure. Therefore, the description of the Book of Numbers – which would refer to the period of the exodus (13th century BC) – is not as historical as we could imagine it, that is, the chronicle of an author coeval to the event and that he carefully records what actually he saw.
Rather, as we have said several times, we are dealing with a projection of supporting elements of the Jewish theology of the sixth century. B.C. in a mythical and founding past, that the post-exilic Judaic community used to define its history and identity. The v. 19 represents another fundamental characteristic of the priestly language, that is the command of YHWH that is punctually executed by his servant Moses. This characteristic is not only linguistic, but also reflects the thought of the priestly class of the time. After the disobedience of the official representatives of the people – i.e. the pre-exiled kings and priests – now everything will have to be carried out and rebuilt in absolute observance of the Law that YHWH gave to Moses.