Read what David L. Stubbs has to say about it:
One of the lessons of Numbers is that encountering God and the things of God is no light thing. God desires to bring blessing to his chosen people, to all nations, and to all creation, and central to this blessing is the gift of God's presence. For us sinful mortals, however, the warmth of God's life-giving presence is also a burning fire that tests us and ultimately cleanses us to make us holy. All this, in fact, is blessing.I like that.