Festal sermons exhibit a distinct mode of creating and communicating knowledge and, hence, constitute one specific element of the late-antique Christian intellectual world. Through their dynamic character and the flexibility of the genre, sermons offered the preacher endless possibilities to spread the word of God and to inspire his audience by drawing them into the liturgical and spiritual world that he created for them. Three elements contributed to this: rhetoric and style; the use of the scriptures; and a theological and liturgical epistemology, in which the sermon transcends the concrete here and now to encompass the past, present, and future of God’s plan of salvation for humanity. The final section shows that the preacher’s liberty was substantial but not unlimited: in the end he remained a servant of the Word and of his congregation.