Catechism of the Catholic Church
154 Believing is possible only by grace and the interior helps of the Holy Spirit. But it is no less true that believing is an authentically human act. Trusting in God and cleaving to the truths he has revealed is contrary neither to human freedom nor to human reason. Even in human relations it is not contrary to our dignity to believe what other persons tell us about themselves and their intentions, or to trust their promises (for example, when a man and a woman marry) to share a communion of life with one another. If this is so, still less is it contrary to our dignity to "yield by faith the full submission of... intellect and will to God who reveals", 26 and to share in an interior communion with him.
155 In faith, the human intellect and will co-operate with divine grace: "Believing is an act of the intellect assenting to the divine truth by command of the will moved by God through grace." 27
English Translation of the Cathechism of the Catholic Church for the United States of America © 1997, United States Catholic Conference, Inc.