Psalms 91:4

He shall cover thee with his feathers
As birds do their young, who cannot cover themselves: this they do from a tender regard to them, whereby they both keep them warm, and protect them from those that would hurt them: this represents the helpless state of the children of God, who are, like to young birds, weak and unable to defend themselves: the tender regard of God unto them, as the eagle and other birds have to their young; see ( Deuteronomy 32:11 ) ( Isaiah 31:5 ) ( Matthew 23:37 ) and the warmth and comforts souls have, as well as protection, under his powerful and gracious presence; he comforts them under their tribulations, as well as defends them from their enemies:

and under his wings shalt thou trust; (See Gill on Psalms 91:1) and the passages there referred to; the same metaphor is continued:

his truth shall be thy shield and buckler;
his faithfulness, which is engaged to keep and preserve his saints safe to his kingdom and glory, ( 1 Corinthians 1:8 1 Corinthians 1:9 ) ( 1 Thessalonians 5:23 1 Thessalonians 5:24 ) , his Son, who is "truth" itself, ( John 14:6 ) , and whose person, blood, righteousness, and salvation, are as a shield and buckler all around the saints, to secure them from ruin and destruction; and are the shield which faith lays hold on, and makes use of, against the temptation, of Satan; see ( Psalms 84:11 ) ( Ephesians 6:16 ) , the word of God also, which is truth, ( John 17:19 ) , every promise in it, and doctrine of it, is as a shield and buckler to strengthen, support, and secure the faith of his people, ( Proverbs 30:5 ) .