because the light of the lantern represent God and nature is close to God. In the second register there are the Angelic Choirs, such as Thrones, Virtus, Angels, Archangels, ect. The third register represents stories of the Genesis, from the Creation of the world to the famous Flood. It is the beginning of the relationship between God and man. The fourth registers shows stories of Joseph the Hebrew, a biblical figure who foreshadows the coming of Christ, because he was able to give Egyptians a salvation, as Christ would give to his people. The fifth register is dedicated to Christ’s life, from the beginning (Annunciation) to the very end (Resurrection). The sixth and last register is that one of Saint John the Baptist, who the Baptistery is dedicated to. Saint John is in the lowest register, so the nearest to us, because he is an intermediary between us and Christ (in the register above it), us and God (represented by the light of the lantern).
So, all the mosaics are an exemple of the salvation we can find following Christ’s life and thanks to the Baptism.
Inside the Baptistery there is also a sort of symbolical passage. In fact, people who were not baptized couldn’t get inside the Cathedral, so they came here to have lessons in preparation to the Baptism. The entered from the Gate of Paradise, the golden door in front of the Cathedral, and they passed on the two beautiful parts of floor that are behind the door to reach the middle of the Baptistery, where the baptismal font was and were they could be baptized. The two parts of the marble floor are decoreted with different subjects: the first one near the Gate of Paradise has animals in the corners, while the second one near the middle of the Baptistery represents a zodiac. So the first is a representation of earth, while the second one of the sky. People who got inside the Baptistery passed from a condition of earth, through a condition of sky, to reach the baptismal font in the middle, where they could find a salvation thanks to Christ (in fact, for Roman Catholics you can’t get inside Heaven without being baptized).
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