Genesis 22:8 - And Abraham said, "My son, God will provide for Himself the lamb for a burnt offering."
John 1:29 - The next day John saw Jesus coming toward him, and said, "Behold! The Lamb of God who takes away the sin of the world!"
The lamb was a sacrificial offering for the ancient Israelites. Their sins were symbolically transferred to the lamb before it was killed and offered up to God as an atonement. The sins of the people were then symbolically forgiven. Jesus was often referred to as the Lamb of God because He became a sacrifice for the sins of mankind.