The interior of the cathedral is a simple, basilica style church with no transepts or side aisles, and a rectangular apse at the end, flanked by two colonnades in the Ionic order.
The high altar is dominated by a huge mosaic of the Madonna of the Immaculate Conception, with the Latin Inscription, “There is no stain in you,” referencing the purity of the Virgin Mary. It is actually a passage from the Song of Solomon, verse 4:7, book in the Old Testament. Christian theology argues there are predictions of Christ and his coming in books of the Old Testament, and this is one such example. Someone has also obviously been looking at Giuseppe Ribera’s Immaculate Conception, as well!
The inscription also has an easy explanation: It comes from the New Testament letter to Titus, “[Thus you] speak the things that suit sound doctrine…,” which was an admonition to the early Church to preach correct teachings to the congregation. St. Joseph and the Christ Child are in the background.
The massive coffered ceiling is typical of a Greek or Roman temple or basilica.
I like the setting off of the Ionic capitals in the pale blue color. The first appearance of the Ionic order was in fact on the interior of Greek temples.
The stained glass windows on either side of the church carry themes of Illinois history on one side…
…and a German emperor or somebody on the other side. I couldn’t figure it out.
The organ and choir loft are also very beautiful.