If you think of your identity and heart as an engine, you could say there is a kind of fuel that powers it cleanly and efficiently—and a kind of fuel that is not only polluting but also destroys the engine.
The dirty fuel is the fuel of fear and the need to prove yourself. Or the need to be needed by someone else. Or the need to express yourself fully and without restraint. There are many “fuels’” that motivate us to live for a time–but only one fuel is clean and will not lead to weariness and disappointment. And that is God’s love for you. Any other fuel will become demonic. It will obsess you or at best merely let you down.
Whenever you’re running your life on those fuels, Satan’s got you where he wants you. The one thing he does not want is that GOd’s words, “You are my beloved child” become the fuel of your life and heart.
Now assurance goes far to set a child of God free. . . .It enables him to feel that the great business of life is a settled business, the great debt a paid debt, the great disease a healed disease, and the great work a finished work; and all other business, diseases, debts, and works, are then by comparison small. In this way assurance makes him patient in tribulation, calm under bereavements, unmoved in sorrow, not afraid of evil tidings; in every condition content, for it gives him a FIXEDNESS of heart. It sweetens his bitter cups, it lessens the burden of his crosses, it smoothes the rough places over which he travels, and it lightens the valley of the shadow of death.
It makes him always feel that he has something solid beneath his feet, and something firm under his hands—a sure friend by the way, and a sure home at the end. . . .There is a beautiful expression in the Prayer-book service for the Visitation of the Sick: “The Almighty Lord, who is a most strong tower to all them that put their trust in Him, be now and evermore thy defence, and make thee know and feel that there is none other name under heaven, through whom thou mayest receive health and salvation, but only the name of our Lord Jesus Christ.”
Timothy Keller, The Great Enemy (Encounters with Jesus Series Book 6).