Is the Immaculate Conception an essential doctrine in Catholicism?

In the *Ineffabilis Deus*, Pope Pius IX states: > Mary ... was > preserved free from all stain of original sin, is a doctrine revealed > by God and therefore to be believed firmly and constantly by all the > faithful. Hence, if anyone shall dare -- which God forbid! -- **to think > otherwise** than as has been defined by us, let him know and understand > that he is **condemned by his own judgment**; that he has suffered > shipwreck in the faith; that he has **separated from the unity of the > Church**; and that, furthermore, by his own action he incurs the > penalties established by law if he should are to express in words or > writing or by any other outward means the errors he think in his > heart. Does this mean that that even if I have confessed my sin, been baptized, and live according to Christ's commands, but I don't believe that Mary was without original sin, then I'm doomed to hell? **If so, why is this an essential doctrine for salvation?** Note that this question asks *if* the Immaculate Conception was necessary for our salvation. I am asking why *belief* in the Immaculate Conception is necessary.