How do you know that John the Baptist's statement about the Lamb of God refers to sacrifice?
John the baptist was Jew, Jews used to offer animal for the atonement of their sin, and this animal shall be slaughtered before the Lord. The animal God used to save the Israelites in the night of the first passover was the lamb(Exodus 20.1-20). The whole assembly of Israel shall slaughter it at twilight. The blood of the lamb must be shed, so it is a sacrifice as it was in ancient time.
How was the comprehensiveness of the "sin of the world" so radical a concept?
It is radical, because the offering of sacrifice was usually for one person, one family or at most for the people of Israel. By saying " the lamb who takes away the sin of the world ", the word "world" includes all kind of human been, even the Israelites' oppressors. How can God send a lamb to take away the sin of even the oppressors of His people: Israel?
