When writing about putting on "the whole armor of God" in Ephesians 6, Paul begins to conclude the passage by repeating the concepts in Luke 21:36—praying always and watching (verse 18). He says in verse 16: ". . . above all, taking the shield of faith with which you will be able to quench all the fiery darts of the wicked one."
Albert Barnes' New Testament Commentaryexplains these fiery darts:
What happens when these fiery darts hit their target? The answer appears in James 1:13-15(Contemporary English Version, CEV):
As Barnes says, these darts "enkindle the worst passions," or as James says, "our desires." Actually, these darts have been flying since the day we were born, doing their damage. Where is it better for us to deal with these darts: at the point of the shield or after they have hit their mark? Of course, at the shield!
II Samuel 22:31 tells us what our shield is: "As for God, His way is perfect; the word of the Lord is proven; He is a shield to all who trust in Him" (see also Genesis 15:1; Psalm 33:20; Proverbs 2:7). We are not the shield. Our faith is not the shield. God is the shield, using the same faith Jesus Christ had. If we let Him, God will protect us in our battles.
How do we erect this "shield of faith?" Notice these verses:
Along with fasting, Christ gives prayer as one of the antidotes to unbelief. David says that running to God for help, of which striving to pray always is the essence, will allow Him to be our shield, our source of power and strength (II Corinthians 3:5; 4:7).
Notice the first part of Matthew 26:41 from the New Life Bible: "Watch and pray so that you will not be tempted. . . ." Jesus repeats the instruction in Luke 21:36 but shows that the same process will build the shield of faith to protect us from the fiery darts of temptation.
Notice that the shield mentioned in Ephesians 6:16 can quench all the fiery darts—not some, not most, but all. Consider the great peace we would have if none of Satan's fiery darts ever reached their intended target! This sheds light on why Christ says in Matthew 11:30: "For My yoke is easy and My burden is light." We know He used every spiritual tool God makes available.
— Pat Higgins
To learn more, see:
Degrading Passions Seeking Stimulation
Fiery Darts of the Wicked One
Shield of Faith
Watch and Pray Always