Catechism of the Catholic Church §221 — excerpt
But St. John goes even further when he affirms that "God is love": God's very being is love. By sending his only Son and the Spirit of Love in the fullness of time, God has revealed his innermost secret: God himself is an eternal exchange…
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.