The windows of the apse carry out the motif of the Trinitarian doctrine of the Christian church. The center window has a triquetra with three equal arcs denotes the equality of the persons of the Godhead. The continuous lines represent their eternal existence, and the interweaving lines express their unity. The equilateral triangle signifies the coequality of the persons in the Godhead and is one of the most commonly used symbols of the Trinity.

Just below the triquetra is the figure of Christ at the time of the Transfiguration, with Moses representing the law and Elijah representing the prophets. The image suggests Christ revealing his divinity and his ministry to the disciples as the one who came to fulfill both the law and the prophecies.

In the lower part of the window is the shield of the Holy Trinity. This shield is a device for expressing the doctrine of the Trinity. At the center is the word Deus (God) and the three surrounding circles are designated: Pater (father), Fioius (Son), and Spiritus Sanctus abbreviated (Holy Spirit). The outer circles are linked to the center by the Latin word est (is). The outer circles join one another with the words non est (is not). In this manner, one may read from any direction without confusion and understand that the Father, Son, and Holy Spirit are each Go, but the Father is not the Son nor the Spirit, and so on until the circle is completed. The center apse window is the most significant of the three, featuring the Trinity with special emphasis on the Fatherhood of God.

The left apse window, as one faces the altar, presents a trefoil at the top, a well-known symbol for the Trinity. It is a modification of three circles of equal size representing the equality of the persons in the Trinity. The figure of Christ with the staff of the shepherd appears in the center of the window symbolizing God’s care for mankind. It is in Christ that God has revealed himself, and hence each of the upper apse windows features his figure. The lower section of the left window is graced with a nativity scene representing the sonship of Christ as the Logos (Incarnate Word), the second person of the Trinity.

The right apse window contains a very significant image at the top. The “all-seeing eye” within a triangle is appropriate in a church window above an altar because it represents the power and omnipresence of God. The triangle conveys an idea of the Trinity in which the Holy Spirit is the third person. While Jesus is the medium of revelation, the Holy Spirit is God present with us, imparting his divine grace to us. Again, the central figure is Christ, emphasizing his place as the revealer of God.

At the bottom of the right window is the symbol for the Holy Spirit. The descending dove with a tri-radiant nimbus is taken from the story of the baptism of Jesus. It was at this time that the Holy Spirit came upon Christ in the form of a dove, symbolizing the reception of special power for his earthly ministry. From the earliest period of the Christian church the symbol of a dove has represented the Holy Spirit.