Catechism of the Catholic Church §2516 — excerpt
Because man is a composite being, spirit and body, there already exists a certain tension in him; a certain struggle of tendencies between "spirit" and "flesh" develops.
This translation is under copyright, so only the cited words are quoted here. Follow the link for the full text. Translation: English translation of the Catechism of the Catholic Church, 2nd ed. (Libreria Editrice Vaticana), as posted at vatican.va.
Also cites: John Paul II, DeV 55