The bible makes bold and daring promises to people of faith. Psalm 91:9-10 says, "Because thou hast made the LORD, which is my refuge, even the most High, thy habitation; There shall no evil befall thee, neither shall any plague come nigh thy dwelling".
A few words for the word "evil" noted in Strong's Hebrew and Greek Dictionary are: evil (naturally or morally), adversity, affliction, bad, calamity, exceedingly, great, grief, harm, heavy, sore, sorrow, trouble, wretchedness, wrong.
In verse four of Psalm 91 the psalmist said, "He shall cover thee with his feathers, and under his wings shalt thou trust: his truth shall be thy shield and buckler."
The shield noted in this Psalms refers to a shield large enough to shield the entire body hence the name thyreos meaning "a gate or door (or "door-shaped"); used of the large, oblong ancient Roman shield (which looked like a full door), large enough to provide full protection from attack (used only in Eph 6:16)."
The word truth refers to God's trustworthiness and faithfulness.In essence, God's trustworthiness and faithfulness surrounds and protects us as a shield. He is the door keeper in our lives keeping out evil, i.e. adversity, affliction, calamity, sorrow, and trouble as we trust him!