John Gill 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)

You shall tread upon the lion and adder
Or be unhurt by such savage and poisonous creatures; as the Israelites, when they travelled through the wilderness, in which were serpents and scorpions; and many of the servants of God has been delivered from them, or have slain them, as Samson, David, and Daniel; and so Christ was among the wild beasts in the wilderness, and yet not touched or hurt by them; and his disciples had power given them by him to tread on serpents and scorpions, and to take up serpents, without receiving any damage from them; and when a viper fastened on the hand of the Apostle Paul, he shook it off, without being hurt by it; see (Mark 1:13) (16:18) (Luke 10:19) (Acts 28:5) ,

it may be understood figuratively of Satan, who, for his voraciousness and cruelty, is compared to a lion; and, for his craft and subtlety, to a serpent, (1 Peter 5:8) (Revelation 12:9) ,

the young lion and the dragon shall you trample underfoot ;
which also may be understood of the great dragon, the old serpent, called the devil and Satan; whom Christ trampled under his feet when he hung on the cross, and spoiled him and his principalities and powers; and who, in a short time, will be bruised under the feet of his people, as he has been already by the seed of the woman, (Genesis 3:15) (Romans 16:20) .