This verse is special to me in a very personal way. I had a moment in my life when I was struggling with my faith. Not my faith for salvation, but my faith for healing from an illness that was sapping my strength. I knew what the Apostle Paul said in Ephesians. "Take up the shield of faith, with which you can extinguish all the flaming arrows of the evil one" (Ephesians 6:16). I felt like the enemy's flaming arrows were hitting me from all sides. I was feeling vulnerable because it seemed like I couldn't find my shield.
God supernaturally impressed me to look up Psalm 91:4. As I prayed I saw it in my mind's eye: Ps. 91:4—just like that! I had no idea what that verse said, but this is what I found. "His faithfulness will be your shield." This verse changed my perspective completely. Instead of struggling to find faith in my faith I realized that His faithfulness was and is my protection. I have faith, but it isn't in my ability to believe. I have faith now in the faithfulness of a Mighty God who will never fail to keep His promises. He has me covered and I find my protection and refuge in Him.
When trouble comes, and that's what this psalm is all about, His faithfulness is there to protect us. "Rampart" is the translation of a Hebrew word that means "to surround." It means that I am not unprotected in any direction. God's faithfulness is my shield and He has me surrounded. I have complete faith in that.