The centerpiece of the Tree of Life is the glorious cross, the throne from which Christ reigns and from which springs a vast acanthus vine. The cross is rooted in the earth and reaches to the dome of heaven, represented by the semicircular bands of color above the cross.
At the top of the cross, we find the Christogram, the Greek letters Chi and Rho, the first two letters of the word Christ. Early Christians adopted this monogram as a symbol of Christianity. On the cross are twelve doves, representing the twelve apostles. Beneath the cross on the left, Mary stands with lowered eyes and hands raised in the orans position of prayer. On the right is John the apostle.
The acanthus vine is an allusion to Christ and the church, based on the words “I am the vine, you are the branches” (John 15:5). Nestlings and birds of every kind, traditional symbols of souls enjoying the happiness of heaven, find their home within the vine. The curling tendrils of the vine terminate in stylized flowers and oil lamps, baskets overflowing with food, and vessels of oil and wine, symbolizing the richness of life in Christ. The unexpected appearance of naked winged sea gods riding on dolphins and Roman Jupiters (pagan images) are signs of the universality of redemption through Christ.
The figures in black and white robes, seated at desks with open books and quills in hand, are the four doctors or theologians of the Latin church: Saints Augustine, Jerome, Gregory, and Ambrose. Beneath the Tree, men and women engage in their daily occupations and workers feed their flocks and herds. They typify the Christian faithful who spend their day-to-day lives within the shelter of the vine that is the church. Nearby are peacocks, emblems of paradise and immortality.
The streams that flow from the foliage at the base of the Tree are symbols of the rivers of the Garden of Eden, which are associated by tradition with the four Gospels, baptism, and the Holy Spirit flowing from Christ to evangelize and nurture the world. Two deer drinking from the streams allude to the soul “thirsting for God” (Psalms 42:1, 63:1).
The text beneath the Tree of Life may be translated: “We compare the church to a vine which withers when rooted in the law but flourishes when rooted in the cross of Christ.” This text also appears in San Clemente.
In the center of the frieze under the painting is the Lamb with a golden halo, symbolizing Christ, and twelve other lambs, symbolizing the apostles. This motif appears in San Clemente and other Roman churches.