9 And it came to pass that we did camp round about the city for many nights; but we did sleep upon our swords, and keep guards, that the Lamanites could not come upon us by night and slay us, which they attempted many times; but as many times as they attempted this their blood was spilt.
I think the imagery of sleeping on ones sword is a very evocative one, and a powerful metaphor for living the Gospel and being prepared against Satan. If the sword represents the word of God and is part of the armor of God, then it suggests continual communion with the word of God. I believe his is both through immersing ourselves in the scriptures and the words of the living prophets, and also through continual personal revelation.
Satan will attempt to stealthily come at night and overwhelm our defenses. He will do so by subtle deceptions which will deceive even the very elect. If we are not prepared, we will be ambushed. We need to be constantly vigilant and cling close to the word of God in order to avoid his deadly attack.