Imagine for a moment that your city is surrounded by enemy forces who aim to destroy you. And you are aware that enemy sympathizers live and work in the city with a view to undermining the city’s defenses. And suppose you discover that there is a song which the enemy and their sympathizers cannot tolerate or approach. Whenever they hear it, they pull back and run the other direction.
Isn’t it certain that you would want to learn this song? And after you learned it, you would sing it when you went to bed at night and when you got up in the morning. You would sing it on the way to work, and whenever you were among strangers. And as your confidence grew you would even venture outside the city and sing it as you walked boldly through the enemy lines on your way to another town. The more deeply embedded in your mind the song became, the more steady and deep and serene and fearless your life would become. Others would see and hear and learn the song from you. And in the end you would conquer the enemy, and there would be no threat at all.
Well, we are surrounded by the enemy—namely, Satan and his forces. He is the father of lies (John 8:44). His weapons are deceit and delusion. His aim is the destruction of your faith and love. And there are enemy sympathizers inside the city of our own souls—namely, the desires of the old self. And there is a song that Satan and his sympathizers cannot tolerate or approach—namely, the song of thanks to God.
Thankfulness is an essential guardian of the soul, and therefore we should guard ourselves with gratitude. We are fair game for the devil when we don’t abound with thanksgiving. Unless the song of thanksgiving is being sung in our hearts the enemy outside will deceive his way into the city of our soul, and the enemy sympathizers within will make his job easy. So for the sake of your own safety, humble yourselves under the mighty hand of God. Receive the wealth of His grace in Jesus Christ. Fill your mouth with thanksgiving. And guard yourselves forever with gratitude!
—John Piper, condensed