I. In the web next to the left wall of the Baptistery is illustrated the first truth of faith contained in the Creed: “CREDO IN DEUM, PATREM OMNIPOTENTEM, CREATOREM CAELI ET TERRAE” (“I believe in God, the Father Almighty, creator of heaven and earth”), testified by the image of the Eternal with His right hand raised heavenwards. In all probability, His left hand, now lost due to deterioration of the fresco, pointed towards the earth. God, immersed in a sphere of light which is emblematic of the world, is thus represented as the creator of all heavenly and earthly things; therefore He shows us with one hand the empyrean and the other the earth, in accordance with a type that recurs insistently in the Sienese cycles illustrating the Creed.
II. The scene next to the back wall, as indicated in the scroll presented by the apostle Andrew, illustrates the second Article of faith: “ET IN IESUM CHRISTUM, FILIUM EIUS UNICUM, DOMINUM NOSTRUM” (“And in Jesus Christ, his only Son, our Lord”). Thus this is the beginning of the illustration of the Creed concerning Jesus Christ, whose figure is rendered in a perfectly frontal position, wrapped in a cloak that opens to reveal the wound in His side.
III. The third web, as the words in the scroll displayed by James the Greater indicate, “QUI CONCEPTUS EST DE SPIRITU SANCTO, NATUS EX MARIA VIRGINE” (“Who was conceived by the Holy Spirit and born of the Virgin Mary”), illustrates the announcement of the Incarnation of the Word made to Mary by the Archangel Gabriel. Corresponding to this, Isaiah, one of the four major prophets, proclaims “ECCE VIRGO CONIPIET ET PARIET FIULIM” (“Behold a virgin shall conceive and bear a son”). This scene shows the Archangel Gabriel, God’s messenger, kneeling in front of the Virgin, who draws back in a gesture of reserve and humility.
IV. In the fourth and last web is shown the Passion and death of Christ: “PASSUS SUB PONTIO PILATO, CRUCIFIXUS, MORTUUS, ET SEPULTUS” (“He suffered under Pontius Pilate, was crucified, died, and was buried”). This article is formulated by the apostle and evangelist John, and is matched by Ezekiel’s prophecy SIGNA THAU… GE[ME]NTIUM (“mark a cross [on the forehead of] the grieving”); according to a venerable tradition widely attested in the patristic writings, the shape of the Greek letter tau corresponds to the cross. This passage from Ezekiel is thus interpreted as a reference to the salvation of mankind through Christ’s sacrifice. In the web we see three moments in the Passion: the flagellation, crucifixion, and burial. The picture is dominated by the first of these episodes: Christ, tied to the column placed in the center of the picture, is beaten while Pilate watches, seated on his faldstool and with a laurel wreath on his head as a symbol of his authority. In the upper section is the crucifixion, while the burial is inserted synthetically into the right corner of the web: Christ is laid in the tomb, with His body wrapped in a winding-cloth.