"the churches grew stronger in faith"

Paul reached also Derbe and Lystra where there was a disciple named Timothy, the son of a Jewish woman who was a believer, but his father was a Greek. The brothers in Lystra and Iconium spoke highly of him, and Paul wanted him to come along with him.

-- Acts 16:1-10

Faith is an entirely free gift that God makes to man. We can lose this priceless gift, as St. Paul indicated to St. Timothy: "Wage the good warfare, holding faith and a good conscience. By rejecting conscience, certain persons have made shipwreck of their faith." To live, grow and persevere in the faith until the end we must nourish it with the word of God; we must beg the Lord to increase our faith; it must be "working through charity," abounding in hope, and rooted in the faith of the Church.

-- CCC 162