'Behold the Lamb of God, who takes away the sin of the world'. This means that

The statement 'Behold the Lamb of God, who takes away the sin of the world' refers to Jesus, and it means that through His death, Christians are cleansed of their sins. The phrase "Lamb of God" is symbolic of Jesus being the ultimate sacrifice, as in the Old Testament times when a lamb was sacrificed to atone for sins. Jesus' death on the cross was the ultimate sacrifice, which took away the sins of the world for all those who believe in Him. Therefore, this statement affirms the Christian belief that Jesus' death on the cross was the ultimate sacrifice and a means of salvation for all believers.