From Scripture we know that the baptismal rite instituted by Christ is a sacramental rite; it is an outward sign instituted by Christ to give grace, a grace that sanctifies the soul and makes it pleasing to God (1 Pet. 3:21; 2 Pet. 1:4). We also read in John 3:5 and Mark 16:16 where Christ says "unless one is born of water and the Spirit, he cannot enter the kingdom of God," and "he who believes and is baptized will be saved." Then we read in Acts 19:1-6 and 22:16; Romans 6:3-4, 11; 1 Corinthians 6:9-11 and 12:13; and Galatians 3:26-27, where Paul says baptism frees us from sin, makes us children of God, gives us new life, and incorporates us into the Body of Christ. In Titus 3:5, Paul again refers to baptism as the "washing of regeneration and renewal by the Holy Spirit," for it signifies and actually brings about the birth of water and the Spirit without which no one "can enter the kingdom of God" (CCC 1215). In Colossians 2:11-12, Paul declares that baptism is "the circumcision of Christ": "In him you were also circumcised, in the putting off of the sinful nature, not with a circumcision done by the hands of men but with the circumcision done by Christ, having been buried with him in baptism and raised with him through your faith in the power of God, who raised him from the dead."
Catholics do not believe in the Protestant doctrine of "once saved always saved." Not only was this teaching never taught in the early Church, there is no biblical basis for it, either.
Every Catholic is called upon by the Church to make a "conscious decision to trust Christ for salvation." But trusting Christ for salvation is not a one-time event (e.g., praying the sinner’s prayer). It is a lifelong commitment. In fact, the Church teaches that "reborn as sons of God, [the baptized] must profess before men the faith they have received from God through the Church and participate in the apostolic and missionary activity of the people of God" (CCC 1270).