1.6. Can the Catholic Church ever fail or teach heresy?
No. The Catholic Church is indefectible — she cannot defect in faith, morals, or worship. Our Lord promised:
“The gates of hell shall not prevail against it.”
“Behold, I am with you all days, even unto the consummation of the world.”
This does not mean individual popes, bishops, or even large parts of the hierarchy cannot fall into error or heresy — history has shown this — but the Church herself, as a divine institution, cannot officially teach heresy in her infallible Magisterium.