The motives, reasons, or grounds for believing in a person, doctrine, or institution.
The Catholic Church claims to be a Divinely-founded institution speaking, in matters of faith and morals, with the certainty and authority of God.
Her credibility rests on the authority of God speaking to her.
She holds that her Founder and Guarantor of her inerrancy, Jesus Christ, is God.
Christ affirmed that He was God.
Mere affirmation, ordinarily, would not confirm such a claim.
Christ proceeded to give proof of His assertion by performing miracles, which are God's seal confirming the person or mission in whose behalf they are performed.
Jesus proclaimed: "I and the Father are one." (John 10)
The Jews accused Him of blasphemy because He claimed to be God.
"Do you say of him whom the Father hath sanctified and sent into the world: Thou blasphemest; because I said: I am the Son of God?
If I do not the works of My Father, believe me not.
But if I do, though you will not believe me, believe the works." (John, 10)
He then proceeded to do what was possible to Divine power alone.
The miracles He wrought were the seal of God on His mission, confirming His claims.
He gave sight to the blind and hearing to the deaf, cleansed the leper, made the cripple whole, commanded the elements, and raised the dead to life.
He it was Who established the Catholic Church, and guaranteed He would be with her to the end of the world.
The Catholic Church is, therefore, the continuation of Christ's ministry.
Her credibility rests on the authority of God Who founded her and guaranteed her against error.
New Catholic Dictionary