Is the Catholic Church the one true Church?

Yes. The Catholic Church teaches that she is the one Church founded by Jesus Christ and entrusted with the fullness of Christian faith, worship, and sacramental life.

What the Church claims. Jesus founded one Church, not a collection of independent denominations. He prayed that His followers would be one (Jn 17:20-23), appointed the Twelve, gave Peter a unique pastoral office, and promised that the gates of hell would not prevail against His Church (Mt 16:18-19; Jn 21:15-17). The Church of Christ subsists in the Catholic Church, governed by the successor of Peter and the bishops in communion with him (CCC 816). She possesses the four marks confessed in the Creed: one, holy, catholic, and apostolic (CCC 811).

What this means for other Christians. Baptized Christians outside full Catholic communion are not simply outsiders. Those who believe in Christ and have been validly baptized are joined to Him and share a real, though imperfect, communion with the Catholic Church (CCC 818). Other Christian communities preserve many gifts from Christ, including Scripture, faith, prayer, Baptism, and, in some cases, valid apostolic ministry and sacraments. These elements of truth and holiness come from Christ and draw people toward Catholic unity (CCC 819).

What "outside the Church there is no salvation" means. All salvation comes from Jesus Christ through His Body, the Church (CCC 846). A person who knows that Christ founded the Catholic Church as necessary and deliberately refuses to enter or remain in her cannot be saved while persisting in that refusal. Yet those who, through no fault of their own, do not know Christ or His Church may attain salvation if they sincerely seek God and respond to His grace (CCC 847). If they are saved, they are saved by Christ and through a mysterious connection with His Church, never apart from Him.

How to respond. This teaching is a call to gratitude, humility, and mission, not pride. Catholics must repent of their sins, pursue holiness, explain the faith charitably, and work for the unity Christ desires (CCC 820-822). If you are considering Catholicism, attend Mass without receiving Communion, read the Gospels, and speak with a Catholic priest about entering full communion.