“A Christian should and must be a cheerful person. If he isn’t, the devil is tempting him. I have sometimes been grievously tempted while bathing in my garden, and then I have sung the hymn, ‘Let us now praise Christ.’ Otherwise I would have been lost then and there. Accordingly, when you notice that you have some such thoughts, say, ‘This isn’t Christ.’ To be sure, he can hear the name of Christ, but it’s a lie because Christ says, ‘Let not your hearts be troubled [John 14:27]. Trust in me,’ etc. This is a command of God: ‘Rejoice!’ I now preach this, and I also write it, but I haven’t as yet learned it. But it happens that we learn as we’re tempted. If we were always glad, the devil would befoul us. Christ knows that our hearts are troubled, and it is for this reason that he says and commands, ‘Let not your hearts be troubled.’ (Luther’s Works, v. 54, p.95)