Why Is Jesus Called the Lamb of God?
After the downfall of Adam and Eve, God tried to find ways for man to atone for his transgressions. Mankind is helplessly doomed that God tried to reach out to save them. The solution He came up with during the Old Testament was the sacrificial system (Leviticus 4:27–31).
The practice is done by presenting a goat, sheep or lamb for offering. Before slaughtering the animal, the sinner would lay his/her hand on its head while confessing his/her sins as a symbolic gesture of transferring the guilt to the offering (verse 29). The animal was then slaughtered because the law required the shedding of its blood for the sinner to obtain forgiveness (Hebrews 9:22).
The ritual's significance is the removal of that person's sins which he/she was supposed to die for. But the animal took his/her place because the sins have been transferred to it. The killing of the animal also signifies the gravity of sin which leads to death (Romans 6:23).
The problem with this practice is that man is so sinful that he had to make sacrifices on a daily basis — an expensive and tedious task considering that livestock didn't come cheap (Hebrews 10:11). So, God had to come up with another means to restore His relationship with man that wouldn't take animal sacrifices anymore.
It had to be a huge one-time sacrifice that would atone for the sins of all souls in one fell swoop (Hebrews 10:12–14). It had to take His own Son's life to accomplish this. John the Baptist described Jesus as the Lamb of God (John 1:29) because the sins of the world were laid upon Him (Isaiah 53:7).
By dying on the cross, Jesus freed man from offering animal sacrifices over and over again (Hebrews 10:17). He became the ultimate one-time sacrificial lamb. Just like the animals in the Old Testament, Jesus shed His blood to wash away the sins of mankind (Matthew 26:28).