They are our inner determinant of right and wrong in our every action. But the uninstructed conscience is no help to right action. We have a personal obligation to form our consciences according to objective moral norms. If you are convinced that God has made a revelation and entrusted it to His Church, you are bound to inquire about that revelation, learn its content, and follow it. No one is a Catholic whose beliefs and conscience are unformed by Catholic teaching.
Protestants tend to forget that.
Mary is the pattern for men who let themselves be opened and gifted by God, of the community of believers, of the Church. A mediator is a go-between. The mediator of the New Covenant is Jesus. He is God and man, so he in his own person spans the chasm between sinful man and God. By his Sacrifice on the Cross,, he pays the debt for his sinful brothers and sisters, our whole human race, and so can offer us reconciliation to the Father.