Q1. How do you know that John the Baptist's statement about the Lamb of God refers to sacrifice? (John 1:29).
Because the Jewish people had been using lambs as sacrifices for their sin, as per the commandment of God. So when John called Jesus the Lamb of God that takes away the sin of the world, he knew exactly what he was saying.
How was the comprehensiveness of "sins of the world" so radical a concept? That He would take away the sins of the world would be radical to the Jewish people. Here they are, sacrifice an expensive and innocent lamb to make atonement for one personal sin. If I had to do this, the blood of lambs would run thick indeed! Yet, Jesus, one Person, one sacrifice, was going to take away all the sins of the world. And He did!