Why did Christ appear at the end of the age?
Christ appeared at the end of the age to put away sin by the sacrifice of Himself. Scripture teaches He entered the holy place once, obtaining eternal redemption for us, not offering Himself repeatedly as the high priest did yearly with the blood of animals.
Les explains that Hebrews 9:26 answers this directly: Christ appeared once in the end of the age "to put away sin by the sacrifice of himself." Unlike the Old Testament high priest who entered the holy place every year with the blood of animals, Christ entered once into the holy place, having obtained eternal redemption for us (Hebrews 9:12). Les contrasts the repeated animal sacrifices with Christ's once-for-all offering. He also points to Hebrews 10:10, where we are sanctified through the offering of the body of Jesus Christ once for all, never to be done again. So Christ's appearance at the end of the age was to deal with sin definitively by His own sacrifice.
For then must he often have suffered since the foundation of the world: but now once in the end of the world hath he appeared to put away sin by the sacrifice of himself.