Your enemy is restless. He never sleeps. He is always going about as a roaring lion, seeking whom he may devour (1 Pet. 5:8). He is ever going to and fro in the earth, and walking up and down in it (Job 1:7). You may be careless about your souls: he is not. He wants them to make them miserable, like himself, and will have them if he can. Surely his enmity is not to be despised?
–Bishop J.C. Ryle, Thoughts for Young Men (p. 13).