The lion is the Bible's image of strength and royalty. Jacob blessed Judah as a lion's whelp, and from Judah's line came the kings — and finally the Messiah, hailed in Revelation as the Lion of the tribe of Juda, who alone is worthy to open the scroll of history. The Lion is the conquering King.
Strikingly, when John turns to see the Lion, he sees instead a Lamb as it had been slain — the Lion conquers by the sacrifice of the Lamb. The Bible also uses the lion for the enemy: your adversary the devil, Peter warns, walketh about as a roaring lion, seeking whom he may devour. But the Lion of Judah has already prevailed, and greater is he that is in us than the roaring foe.
The Lion in Scripture
And one of the elders saith unto me, Weep not: behold, the Lion of the tribe of Juda, the Root of David, hath prevailed to open the book, and to loose the seven seals thereof.