Catechism of the Catholic Church §2700 — excerpt
Through his Word, God speaks to man. By words, mental or vocal, our prayer takes flesh. Yet it is most important that the heart should be present to him to whom we are speaking in prayer: "Whether or not our prayer is heard depends not…
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: St. John Chrysostom, Ecloga de oratione 2: PG 63, 585