What is the magisterium and why is it needed?

The Magisterium is not established to resolve disputes between men; it is established to determine the direction of the Church related to supernatural things, like the Creed, the Morals, the Law, the Liturgy.

The Magisterium is necessary, because by ourselves we are not able to find the right way. God may correct our bona fide errors, and give a person salvation regardless of errors, but God wants the Magisterium to be the solid base (rock) for the Catholic Church, and through that for the whole world.