The New Law practices the acts of religion: almsgiving, prayer and fasting, directing them to the "Father who sees in secret," in contrast with the desire to "be seen by men." Its prayer is the Our Father.
-- CCC 1969
Jesus' call to conversion and penance, like that of the prophets before him, does not aim first at outward works, "sackcloth and ashes," fasting and mortification, but at the conversion of the heart, interior conversion. Without this, such penances remain sterile and false; however, interior conversion urges expression in visible signs, gestures and works of penance.
-- CCC 1430
(See also CCC 575, 1434, 1755, 2043.)