From the Catechism:
The Church, "the pillar and bulwark of the truth", faithfully guards "the faith which was once for all delivered to the saints". She guards the memory of Christ's words; it is she who from generation to generation hands on the apostles' confession of faith.As a mother who teaches her children to speak and so to understand and communicate, the Church our Mother teaches us the language of faith in order to introduce us to the understanding and the life of faith."
The faith "which was once for all delivered to the saints" is our key to heaven.
God in his wisdom sees to it that this faith is preserved and guarded and kept pure.
Where else but within the protection of the very Church he founded? "Peter you are rock, and upon this rock, I will build my Church."