John Piper, Future Grace (Sisters, OR: Multnomah, 1995), pp. 55, 56:
Suppose you are in a car race and your enemy, who doesn’t want you to finish the race, throws mud on your windshield. The fact that you temporarily lose sight of your goal and start to swerve, does not mean that you are going to quit the race. And it certainly doesn’t mean that you are on the wrong race track. Otherwise the enemy wouldn’t bother you at all. What it means is that you should turn on your windshield wipers and use your windshield washer.
When anxiety strikes and blurs our vision of God’s glory and the greatness of the future that he plans for us, this does not mean that we are faithless, or that we will not make it to heaven. It means our faith is being attacked. At first blow, our belief in God’s promises may sputter and swerve. But whether we stay on track and make it to the finish line depends on whether, by grace, we set in motion a process of resistance—whether we fight back against the unbelief of anxiety. Will we turn on the windshield wipers and will we use our windshield washer?
. . . 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, as we have seen, is “by the Spirit and by faith in the truth” (2 Thess 2:13). The work of the Spirit and the Word of the 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 (Jer 29:11), our faith grows stronger and the swerving anxiety smooths out.