CCC 787 From the beginning, Jesus associated his disciples with his own life, revealed the mystery of the Kingdom to them, and gave them a share in his mission, joy, and sufferings.¹ Jesus spoke of a still more intimate communion between him and those who would follow him: “Abide in me, and I in you. .. I am the vine, you are the branches.”² And he proclaimed a mysterious and real communion between his own body and ours: “He who eats my flesh and drinks my blood abides in me, and I in him.”³

CCC 1423 It is called the sacrament of conversion because it makes sacramentally present Jesus’ call to conversion, the first step in returning to the Father⁴ from whom one has strayed by sin.
It is called the sacrament of Penance, since it consecrates the Christian sinner’s personal and ecclesial steps of conversion, penance, and satisfaction.

CCC 1427 Jesus calls to conversion. This call is an essential part of the proclamation of the kingdom: “The time is fulfilled, and the kingdom of God is at hand; repent, and believe in the gospel.”⁵ In the Church’s preaching this call is addressed first to those who do not yet know Christ and his Gospel. Also, Baptism is the principal place for the first and fundamental conversion. It is by faith in the Gospel and by Baptism⁶ that one renounces evil and gains salvation, that is, the forgiveness of all sins and the gift of new life.

CCC 2612 In Jesus “the Kingdom of God is at hand.”⁷ He calls his hearers to conversion and faith, but also to watchfulness. In prayer the disciple keeps watch, attentive to Him Who Is and Him Who Comes, in memory of his first coming in the lowliness of the flesh, and in the hope of his second coming in glory.⁸ In communion with their Master, the disciples’ prayer is a battle; only by keeping watch in prayer can one avoid falling into temptation.⁹

1 Cf. Mk 1:16-20; 3:13-19; Mt 13:10-17; Lk 10:17-20; 22:28-30.
2 Jn 15:4-5.
3 Jn 6:56.
4 Cf. Mk 1:15; Lk 15:18.
5 Mk 1:15.
6 Cf. Acts 2:38.
7 Mk 1:15.
8 Cf. Mk 13; Lk 21:34-36.
9 Cf. Lk 22:40, 46.