The purpose of this study is to explore two aspects of the oratorio Jephte by Giacomo Carissimi: first is the manner in which Carissimi used The Doctrine of the Affections to organize the music textually, and second is the way in which Carissimi employed The Doctrine of the Affections to evoke Roman Catholic devotion. In the oratorio Jephte, Carissimi followed the affective characteristics in the modes and intervals, which Gioseffo Zarlino, in his book Le Istitatione Harmoniche (1558), and Nicola Vicentino, in his book L’antica musica (1555), discussed in the early sixteenth century. For the purpose of expressiveness, Carissimi used three prominent compositional techniques: paired transposition, mutatio toni, and mutatio modi. The Counter-Reformation movement of the sixteenth century Catholic Church gave birth to the devotional musical genre, oratorio. Carissimi, as a master of the Roman School of composition, infused a pious quality throughout the whole work of the oratorio Jephte, using the Doctrine of the Affections. The analysis explores Carissimi’s usage of the Doctrine of the Affections in the oratorio Jephte to musically express the devotional nature of the Biblical story. The primary modes employed in the oratorio Jephte are Mixolydian, Ionian, Aeolian, and Phrygian; each mode represents specific characters. Moreover, through the use of intervallic affective characteristics, Carissimi transmits the concrete emotional properties of the text to the music. In the last movement of Jephte, Carissimi also used symbolism to give a moral message to the listeners.