Altarpiece in Il Gesu'

Interior art and architecture of Il Gesu' exhibits the ideas and doctrines that were confirmed by the Council of Trent. During the second council the doctrine of transubstantiation was debated and eventually accepted by the Church. Transubstantiation, a doctrine widely refuted by the emerging Protestant church, is the belief that the elements in the Eucharist are converted to the body and blood of Christ at their consecration. Counter Reformation architecture began to incorporate transubstantiation into the designs.

Il Gesu', the model for countless Jesuit churches exemplifies how Counter Reformation architecture displayed this Church doctrine. The Eucharist, one of the seven sacraments established at the Council of Trent, occurs during the celebration of the mass at the altar. Il Gesu' was built between 1568 and 1584, the height of the implementation of church reform as decided by the Council. when a visitor enters the church the side chapels are closed off architecturally and the eyes are immediately drawn down the long nave to the altar. All attention is given to the altar, the place where the sacrament of the Eucharist is carried out and consecrated. The placement and prominence of the altar exemplify the Church's ability to assert their beliefs and doctrine adamantly refuted by Protestants.

The Council desired for architecture to represent the theological doctrines, as well as Biblical stories. The altarpiece at this church is a clear example of the Church, during its reforming years, establishing those doctrines within the architecture to reaffirm their importance in the faith.