The Catechism in Questions & Answers

240. How does a human being come to believe?

Faith always starts with God, who reveals Himself through His word and His works. Faith is a gift of God. True faith is based on God’s grace of election. At the same time, faith is an obligation for human beings. Whether and to what degree a human being comes to believe is also dependent on his own effort: a person must want to believe. For this reason it is necessary to pray for faith.

“Lord, I believe; help my unbelief!”
Mark 9: 24