Paul says that, “above all,” we are to take up the shield of faith.
“Above all, taking the shield of faith, wherewith ye shall be able to quench all the fiery darts of the wicked” (Eph. 6:16).
This passage tells us a great deal about the nature of our spiritual conflict. When two adversaries clash on the field of battle, there are two things to consider. The first is what you are trying to do to him, and the second is what he is trying to do to you. What are your tactics against him (prayer for all the saints, and for gospel preaching), and what are his against you (the firing of doubts)?
This verse says we are up against the wicked one, who was earlier identified as the devil (v. 11), against the principalities and powers (v. 12). We can infer that he is flinging doubts because the shield that extinguishes his darts is the shield of faith.
So then, what is faith?
“Now faith is the substance of things hoped for, the evidence of things not seen . . . Through faith we understand that the worlds were framed by the word of God, so that things which are seen were not made of things which do appear” (Heb. 11:1-3).
And there is another layer beneath that. Faith is the natural response to the perceived faithfulness of God.
“Through faith also Sara herself received strength to conceive seed, and was delivered of a child when she was past age, because she judged him faithful who had promised” (Heb. 11:11).
We all believe the chair we are sitting in will hold us, but our faith doesn’t hold us. The chair holds us or, put another way, the faithfulness of the chair holds us. We all believe that the roof over our heads will not crash in on us, but our collective faith isn’t holding the roof up. The beams hold the roof up. Our faith can get us on the plane, but the wings make it stay aloft. This is why someone with mustard seed faith can fly safely to their destination, and someone with total faith can crash. Everything depends upon the faithfulness of the object.
Faith in God in our day is under assault in two major areas as my son Nate has pointed out. Those two areas are evolution and the problem of evil. Notice how both of those are addressed here in Hebrews. By faith we understand that the worlds were framed by the word of God (v. 3). And by faith we understand that the one who comes to God must believe that He is, and is the rewarder of those who diligently seek Him (v. 6). This last point addresses the problem of evil. There is a moral order in the world, and it is not a blind machine that chews up nice people and evil people alike. God rewards the one who pursues him.
Two principal darts, employed in our day quite effectively, are those of rationalistic science and nihilistic philosophy.
One last point. We must always distinguish doubts from questions. Questions should be answered, doubts deflected. You should use a shield on doubts, but if you use a shield on questions, the result will be a pathetic anti-intellectualism. And if you try to answer doubts, you are going to be mortally wounded by the one who throws those fiery darts.