John Calvin Commentary Psalms 91:4

"He will cover thee with his pinions, And under his wings shalt thou take refuge: His truth is a shield and a buckler." — Psalms 91:4 (ASV)

He shall protect you with his wings. This figure, which is employed in other parts of Scripture, is one that beautifully expresses the singularly tender care with which God watches over our safety. When we consider the majesty of God, there is nothing that would suggest a likeness such as is drawn here between him and the hen or other birds, who spread their wings over their young ones to cherish and protect them.

But, to accommodate our infirmity, he does not hesitate to descend, as it were, from the heavenly glory that belongs to him, and to encourage us to approach him under so humble a similitude. Since he condescends so graciously to our weakness, surely there is nothing to prevent us from coming to him with the greatest freedom.

By the truth of God, which, the Psalmist says, would be his shield and buckler, we must understand God’s faithfulness, meaning he never deserts his people in their time of need. Still, we cannot doubt that he also had in mind the Divine promises, for it is only by looking to these that anyone can venture to cast themselves upon God’s protection.

Since, without the word, we cannot come to the enjoyment of that Divine mercy about which the Psalmist had already spoken, he now comes forward himself to bear witness to it. Formerly, under the comparison of a fortress, he had taught that by trusting in God we will enjoy safety and security; now he compares God to a shield, intimating that he will come between us and all our enemies to preserve us from their attacks.