13 Wherever God opens a door of speech for proclaiming the mystery of Christ (cf. Col. 4:3), there is announced to all men (cf. Mark 16:15; 1 Cor. 9:15; Rom. 10:14) with confidence and constancy (cf. Acts 4:13, 29, 31; 9:27, 28; 13:46; 14:3; 19:8; 26:26; 28:31; 1 Thess. 2:2; 2 Cor. 3:12; 7:4; Phil. 1:20; Eph. 3:12; 6:19, 20) the living God, and He Whom He has sent for the salvation of all, Jesus Christ (cf. 1 Thess. 1:9-10; 1 Cor. 1:18-21; Gal. 1:31; Acts 14:15-17, 17:22-31), in order that non - Christians, when the Holy Spirit opens their heart (cf. Acts 16:14), may believe and be freely converted to the Lord, that they may cleave sincerely to Him Who, being the "way, the truth, and the life" (John 14:6), fulfills all their spiritual expectations, and even infinitely surpasses them. This conversion must be taken as an initial one, yet sufficient to make a man realize that he has been snatched away from sin and led into the mystery of God's love, who called him to enter into a personal relationship with Him in Christ. For, by the workings of divine grace, the new convert sets out on a spiritual journey, by means of which, already sharing through faith in the mystery of Christ's Death and Resurrection, he passes from the old man to the new one, perfected in Christ (cf. Col. 3:5-10; Eph. 4:20-24). This bringing with it a progressive change of outlook and morals, must become evident with its social consequences, and must be gradually developed during the time of the catechumenate. Since the Lord he believes in is a sign of contradiction (cf. Luke 2:34; Matt. 10:34-39), the convert often experiences an abrupt breaking off of human ties, but he also tastes the joy which God gives without measure (cf. 1 Thess. 1:6). The Church strictly forbids forcing anyone to embrace the Faith, or alluring or enticing people by worrisome wiles. By the same token, she also strongly insists on this right, that no one be frightened away from the Faith by unjust vexations on the part of others. In accord with the Church's ancient custom, the convert's motives should be looked into, and if necessary, purified.
Source: Ad Gentes (Vatican.va)