Martin Lloyd-Jones’ book Spiritual Depression has had a profound impact on my life. It is a compilation of his sermons from the book of Psalms. In his sermon on Psalm 42, he sets forth what he believes is the fundamental cause of all our unhappiness and prescribes a cure.

“Have you realized that most of your unhappiness in life is due to the fact that you are listening to yourself instead of talking to yourself? Take those thoughts that come to you the moment you wake up in the morning. You have not originated them, but they start talking to you, they bring back the problems of yesterday, etc. Somebody is talking. Who is talking to you? Your self is talking to you. Now this man’s (Psalm 42:5,11) treatment was this; instead of allowing this self to talk to him, he starts talking to himself. ‘Why are you cast down, O my soul?’ he asks. His soul had been depressing him, crushing him. So he stands up and says: ‘Self, listen for a moment, I will speak to you.’ … You have to take yourself in hand, you have to address yourself, preach to yourself, question yourself. You must say to your soul: ‘Why are you cast down’ – what business have you to be disquieted? You must turn yourself on, upbraid yourself, exhort yourself, and say to yourself: ‘Hope in God’ – instead of muttering in this depressed, unhappy way. And then you must go on to remind yourself of God, who God is, and what God is and what God has done, and what God has pledged Himself to do. Then having done that, end on this great note: defy yourself, and defy other people, and defy the devil and the whole world, and say with this man: ‘I shall yet praise Him for the help of His countenance, who is also the health of my countenance and my God.’”

— From the book, Spiritual Depression, by Martin Lloyd Jones, pp. 20-21