John Calvin Commentary Psalms 91:13

"Thou shalt tread upon the lion and adder: The young lion and the serpent shalt thou trample under foot." — Psalms 91:13 (ASV)

Thou shalt walk over the lion and asp. The same truth is expressed here in different words. He had already spoken of the obstacles which Satan throws in our course under the figure of a stone. Now he speaks of the formidable troubles to which we are exposed in the world under the figures of the asp, lion, young lion, and dragon; for as long as we are here, we may truly be said to walk among wild beasts and those that threaten us with destruction.

And in this situation, what would become of us if God did not promise to make us victorious over the many evils that everywhere threaten us? No one who seriously considers the temptations to which he is liable will wonder that the Psalmist, in order to remove apprehension from the minds of the Lord’s people, adopted the language of hyperbole. Nor, indeed, will such a person say it is hyperbole, but rather a true and exact representation of their case.

We boast much of our courage as long as we remain at a distance from the scene of danger; but no sooner are we brought into action, than in the smallest matters we conjure up for ourselves lions, dragons, and a host of frightful dangers. The Psalmist accommodates his language to this infirmity of our carnal apprehension. The Hebrew word שחל, shachal, which in the Septuagint is translated as asp, means a lion; and such repetition in the second part of the sentence is common in Hebrew. Therefore, there is no need to look for any subtle distinction that may have been intended in specifying these four different kinds of animals. By the lion and young lion we are clearly to understand more open dangers, where we are assailed by force and violence; and by the serpent and dragon, hidden evils, where the enemy attacks us insidiously and unexpectedly, like a serpent from its lurking place.