One of the central words of the parsha is zva. G-d command moshe to count all the males over age 20 who may go out "zva". Rashi is quoted by the Ramban as saying that yotzeh zva means those who can go to war. But the Ramban suggests an alternate meaning: those who go out to join the community, kehila. How does this meaning fit to the word zva?
The primary need of man is to be social. As aristotle says, man is the political animal. Since man cannot survive alone, he must form groups. And these groups must be governed, ordered or at least follow some rules. So man is an animal requiring political structures. Man makes communities. An army is an occasional function of the community. You certainly cannot have an army with out people first joining togetehr in some sort of politcal fashion.
In english translations of the Homer you will see the word Host used to apply to an enemy army. But a Host in also a joining of people. To host some one is to bring him into your community. The word retains this double meaning, community and the army of the community. The army is just one type of coming together of a people to form a community.
If you look at the word "zva" it is composed of two word ze and ba. "go out" and "come in" An army is on the one hand a coming in together of people for a unifying purpose. But it is for the purpose of going out to meet the enemy in the field. All actions of a kehila, community are first coming togethers and then doing some action, going out, together. Thus zva can mean army or community of any type.
In this sense Moshe is counting the Jewish poeple. G-d is about to set the schina down on the community. God will settle only on a people that has first come together as a community. Thus the counting. Each person must give his half shekel and join the community. Especially for a holy structure like a mishkan, the community must be united, not for violence, but for Godliness.
For similar non-violent usage of the word zva , see 4:23