The first two stanzas are metaphorical, about Christian homes being assaulted by outside evil influences. The last two stanzas are more about survivalism.
The modern world that surrounds us is extremely fragile. A century of civilized progress can be suspended in a very short time by a serious natural disaster, plagues, atomic bombs or electro-magnetic pulse. Even a bad trucking strike would empty all the shelves at the local grocery stores in a couple of days. Most people use debit cards, but if the power grid goes down nobody is buying anything soon. Having a few weeks worth of extra canned food and water stored away is a smart idea.