Chapter 1 – the witness of John the Baptist: verse 29, “Behold the lamb of God who takes away the sin of the world!”
Under the Mosaic Law a sacrifice was required for sin with the 1 year old unblemished male lamb being the most common sacrificial animal. Also, the Jew’s annual Passover celebration commemorated their release from slavery in Egypt when they sacrificed the lamb, ate it, and sprinkled its blood on the doorpost of their house. The destroying angel, “passed over” and did not kill the firstborn of that household, whether a son or a male animal. Over the course of the Israelite’s history, 100’s of thousands, perhaps millions of lambs had been sacrificed for the sins of the people. And now God is providing His perfect first born Son to be sacrificed for the sin (all ever) of the world.
The writer John records in the same chapter, “He came to His own [the Jewish people] and those who were His own, did not receive Him. But as many as received Him, to them He gave the right to become children of God, even to those who believe on His name.” (1:1-12). John invites us to believe in Jesus, receive His forgiveness and become a child of God.