‘Take you (ye) the sum of all the congregation of the children of Israel, by their families, by their fathers' houses, according to the number of the names, every male, by their heads, from twenty years old and upward, all that are able to go forth to war in Israel, you (thou) and Aaron shall number them by their hosts.'
The command is given to ‘take the sum' of all men of military age in the twelve tribes (excluding Levi), in ‘the congregation of the children of Israel', numbering them in their different regiments (‘hosts'). The intention was in order to organise the different sections of the army. This was ‘the Lord's army'. What pride there probably was in its being numbered. What sad failure would result when as a result of unbelief it would flee from the Amorites. And yet God's purposes would go forward and success would come in the end, not through the size of that army but through God's power at work through weakness.
This numbering was to be done ‘by their families, by their father's houses', in other words ‘wider family by wider family', and ‘tribe by tribe'. Each section would number its men available for action and the numbering would then be accumulated to give the number for the tribe. The numbering was to be of those available to ‘go forth to war'.
“The congregation of Israel.” A regular description for the tribes of Israel as a whole seen as one in their submission to Yahweh, seen as a people ‘gathered' to serve Him. Sometimes it can refer to the mature menfolk, or sometimes to the whole of Israel.
“According to the number of the names.” This may refer to the names of the twelve tribes. But more probably it simply refers to the people as ‘names' as it refers to them as ‘heads' and ‘every male' (compare Numbers 1:17). They are not just numbers, they have names. Compare Numbers 26:53.
We note that the command was given to Moses, but that Aaron was also to be involved in the matter in his new position as ‘the Priest' (the High Priest). This linking is stressed in the passage Numbers 1:1 to Numbers 3:1 related to numbering (see Numbers 1:3; Numbers 1:17; Numbers 1:44; Numbers 2:1), although Moses alone is mentioned where Yahweh's direct command is stressed (Numbers 1:19; Numbers 1:48; Numbers 1:54; Numbers 2:33-34). This is officially ‘the history of Moses and Aaron' as confirmed by the colophon (Numbers 3:1).