He's perfectly loving, but He's also perfectly just, and perfect justice doesn't let the guilty go free. And we're all guilty of many things. A perfectly just God cannot allow sin to go unpunished without ceasing to be perfectly just. But because of His perfect love, He cannot stand to be apart from us, either. Now He has a dilemma.
Perfect justice demands a penalty but perfect love demands reconciliation.
So He decided to pay the price Himself. He came to Earth in the form of a Man, Jesus Christ, the Son of God. And He willingly went to the cross, allowing Himself to be executed to pay the price for our sin. Here's the rest of the passage I quoted above. The Book of Isaiah was written centuries before the birth of Christ.