John the Baptist saw Jesus coming toward him and said, “Behold, the Lamb of God, who takes away the sin of the world."
Today, John the Baptist gives us the most important testimony: by pointing out that Jesus is the "Lamb of God", he is telling us that He is the Son of God who is coming to save us and forgive our sins. Old Israel sacrificed lambs and other animals as offerings to God for His forgiveness. They used to say that their blood washed our sins. But... it was just the blood of animals.
-Jesus washed our impurities in the Cross: the Blood of "God incarnate" was the only blood able to purify us.