Olivier Messiaen was a prominent twentieth-century French composer. His musical language includes highly complicated concepts derived from a variety of sources. Hindu rhythms, Greek rhythms, and bird calls influenced him deeply; his Catholic faith, however, had the greatest impact on his compositions. I provide a detailed analysis of two religiously motivated pieces from his Vingt Regards sur l'Enfant-Jesus (Twenty Gazes upon the Infant Jesus), one of the most remarkable solo piano works of the twentieth-century, to explore how he integrates the Christian theology into his musical language. Je dors, mais mon c¿ur veille (I sleep but my heart waketh) is a dialogue that represents Messiaen's mystic love of God, whereas Regard des Anges (Gaze of the Angels) is a celebration symbolizing the angels beholding the birth of Jesus Christ. I explain how the entirely different subjects of the two pieces are articulated in the change of pitch collections and rhythmic structures, as well as how the changes of musical language through the use of the different pitch collections generate the formal structure that is related to the biblical source. ""Cagdas Soylar's study represents a valuable contribution to modern Messiaen research. It will benefit anyone wishing to explore in detail Messiaen's style, musical vocabulary, and deep spirituality. Through detailed and scholarly examination of two of his Vingt Regards sur l'Enfant-Jesus, Ms. Soylar unpacks Messiaen's faith integration worldview--i.e. ways in which his deep religious beliefs are portrayed in his music--and suggests implications for performance."" --Eugene Alcalay, Steinway Artist; Fulbright Scholar; President of the American Liszt Society, Southern California Chapter; Professor of Piano at Azusa Pacific University Cagdas Soylar completed her doctoral degree in piano performance at Yasar University in Izmir, Turkey. She earned two master's degrees in piano performance at Pittsburg State University, and in collaborative piano at Azusa Pacific University. Winner of several piano competitions and recipient of numerous awards in the United States, she has performed extensively as a solo and collaborative pianist in China, Canada, and many countries in Europe; she is currently living in the Greater Los Angeles Area.