Where/when did God give this authority to the Catholic Church?
Is the Magesterium of the church made up of individuals or one individual? If so, then how can they interpret the Bible, but other individuals cannot? Are they infallible?
He gave them the authority when He gave them the power to bind and loose....the magesterium is made up of individuals under the guidance of one individual. In certain matters they are infallible and no other individuals in history have ever been granted that authority...they can interpret the bible because the Holy Spirit inspires their decisions.