Do not be anxious about anything, but in everything by prayer and supplication with thanksgiving let your requests be made known to God. (Philippians 4:6)
When I am anxious about my ministry being useless and empty, I fight unbelief with the promise of Isaiah 55:11. “So shall my word be which goes forth from my mouth; it shall not return to me empty, without accomplishing what I desire, and without succeeding in the matter for which I sent it.”
When I am anxious about being too weak to do my work, I battle unbelief with the promise of Christ, “My grace is sufficient for you, for power is perfected in weakness” (2 Corinthians 12:9).
When I am anxious about decisions I have to make about the future, I battle unbelief with the promise, “I will instruct you and teach you in the way which you should go; I will counsel you with my eye upon you” (Psalm 32:8).
When I am anxious about facing opponents, I battle unbelief with the promise, “If God is for us, who is against us!” (Romans 8:31).
When I am anxious about the welfare of those I love, I battle unbelief with the promise that if I, being evil, know how to give good things to my children, how much more will the “Father who is in heaven give what is good to those who ask him!” (Matthew 7:11).
And I fight to maintain my spiritual equilibrium with the reminder that everyone who has left house or brothers or sisters or mother or father or children or farms, for Christ’s sake “shall receive a hundred times as much now in the present age, houses and brothers and sisters and mothers and children and farms, along with persecutions; and in the age to come, eternal life” (Mark 10:29–30).
When I am anxious about being sick, I battle unbelief with the promise, “Many are the afflictions of the righteous but the Lord delivers him out of them all” (Psalm 34:19).
And I take the promise with trembling: “Tribulation brings about perseverance; and perseverance, proven character; and proven character, hope; and hope does not disappoint, because the love of God has been poured out within our hearts through the Holy Spirit who was given to us” (Romans 5:3–5).
John Piper, Future Grace, pages 60–61