The Bible calls Jesus BOTH the Lamb of God and the Lion of the tribe of Judah. There is nothing casual about that.
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. (Rev 5:5)
This was prefigured in the prophecy of Jacob (Gen 49:9-12) before he died, where Jesus is called "Shiloh":
Judah is a lion's whelp: from the prey, my son, thou art gone up: he stooped down, he couched as a lion, and as an old lion; who shall rouse him up? The sceptre shall not depart from Judah, nor a lawgiver from between his feet, until Shiloh come; and unto Him shall the gathering of the people be. Binding His foal unto the vine, and His ass's colt unto the choice vine; He washed his garments in wine, and His clothes in the blood of grapes: His eyes shall be red with wine, and His teeth white with milk.
The first title refers to His first coming, and the second title refers to His second coming. There is absolutely no conflict. Christ came as the Lamb of God to die for the sins of the whole world. But when He comes the second time He comes to destroy all the enemies of God, Christ, Christians, and Israel. It is only after that that Christ sets up His eternal Kingdom on earth. Thus He comes as a Lion. This time is called "the day of vengeance of our God".