Cast all your anxieties on him, for he cares about you. (1 Peter 5:7)
Psalm 56:3 says, “When I am afraid, I put my trust in thee.”
Notice: it does not say, “I never struggle with fear.” Fear strikes, and the battle begins. So the Bible does not assume that true believers will have no anxieties. Instead the Bible tells us how to fight when they strike.
For example, 1 Peter 5:7 says, “Cast all your anxieties on Him, for He cares about you.” It does not say, you will never feel any anxieties. It says, when you have them, cast them on God.
When the mud splatters your windshield and you temporarily lose sight of the road and start to swerve in anxiety, turn on your wipers and squirt your windshield washer.
So my response to the person who has to deal with feelings of anxiety every day is to say: that’s more or less normal. At least it is for me, ever since my teenage years. The issue is: How do we fight them?
The answer to that question is: we fight anxieties by fighting against unbelief and fighting for faith in future grace. And the way you fight this “good fight” is by meditating on God’s assurances of future grace and by asking for the help of his Spirit.
The windshield wipers are the promises of God that clear away the mud of unbelief, and the windshield washer fluid is the help of the Holy Spirit. The battle to be freed from sin . . . is “by the Spirit and faith in the truth” (2 Thessalonians 2:13).
The work of the Spirit and the Word of truth. These are the great faith-builders. Without the softening work of the Holy Spirit, the wipers of the Word just scrape over the blinding clumps of unbelief.
Both are necessary—the Spirit and the Word. We read the promises of God and we pray for the help of his Spirit. And as the windshield clears so that we can see the welfare that God plans for us (Jeremiah 29:11), our faith grows stronger and the swerving of anxiety smooths out.
~John Piper, Future Grace, Multnomah Books (Colorado Springs, CO), page 56