Catechism of the Catholic Church

In keeping with the Lord's command, the Gospel was handed on in two ways: - orally "by the apostles who handed on, by the spoken word of their preaching, by the example they gave, by the institutions they established, what they themselves had received-whether from the lips of Christ, from his way of life and his works, or whether they had learned it at the prompting of the Holy Spirit"; - in writing "by those apostles and other men associated with the apostles who, under the inspiration of the same Holy Spirit, committed the message of salvation to writing."