God's promises are sure and true. In Psalm 91 they are specific too. God promises to protect from secret traps and deadly diseases. This doesn't mean, however, that we have an "automatic protection" from every snare or pestilence, but rather a time to remember all the times God's faithfulness and protection have prevailed. That's an interesting thought isn't it? How many times has God's protection kept us, His people, from something meant to do us evil? This side of heaven we may never know. What we do know is that God's protection is certain - eternally certain. As Martin Luther once said, "...it is our faith that makes us the little chick and God the protective hen where we can hide, hope and hover under the protection of His wings, for there is health in His wings."* That truth and surety gives us confidence to face what ever comes our way knowing that God will see us through the storm. Our faith will be stronger because of it as we keep our eyes on Him!
John Trapp commentary on Psalm 91:4 - Here is the full footnote: V: 4. He shall cover thee with his feathers As the hen doth her chickens; Fides est quae te pullastrum, Christum gallinam facit, ut sub pennis eius speres; nam salus in pennis eius, saith Luther; it is faith which maketh thee the little chicken, and Christ the hen; that thou mayest hide, and hope, and hover, and cover under his wings; for there is health in his wings.