"The Lamb of God"

The Van Eycks were among the first to work with oil paint.

The Lamb of God is van  Eyck's larger Altar piece renowned for its intricate details, luminous colors, and the meticulous brushwork technique. The central panel depicting a sacrificial lamb, symbolizes Jesus Christ, who is surrounded by angels and worshippers. The Lamb of God embodies the concepts of salvation and redemption, and has influenced countless artists throughout history.

The lamb, bleeding from its neck is symbolic for Jesus sacrificing his life in order to redeem humankind from its sins. People gather around from everywhere to watch the show, just as they did when Jesus was crucified. The blood of the lamb (i.e. innocence) flows into a chalice: this explains the symbolic drinking of wine at church services.
The term Lamb of God is found in John 1:29: The next day John saw Jesus coming toward him and said, "Look, the Lamb of God, who takes away the sin of the world!"
Further on, in the Revelation of John, the lamb plays a key role.
The Latin term for Lamb of God is Agnus Dei.