Define Christianity

[Polaris]

All of it. Merely believing in Jesus is just the first step of many.

The significance of three days was the time, according to Jewish tradition, that it took for the soul to leave the body. If it was less than three days, according to their tradition, Jesus would not have been truly dead.

BTW, Catholic Church means the universal (from the Greek) Church. So not the Catholic Church as in the actual physical organization.

The Holy Spirit is central to Christianity. There would be no Christians without.

I reject your definition as being overly exclusive from an outsider's prospective.  I have to deal with those who consider themselves Christian and they don't all fit your definition.  And if somehow, Jesus were the man portrayed in the Gospels, I think he'd disagree with you.  I doubt that belief in three days or the holy spirit would matter much to him.

Yes I know that catholic means universial, but the creed is determined to limit faith to a much smaller group than the "universal."  I use to enjoy telling the uneducated that my reading tastes were catholic, which they are.  But they aren't Roman Catholic.

Jesus stated the only unforgiverable sin would be the denial of the Holy Spirit.

It only limits the heretical groups of which none exist from that time; there are a couple new ones like JW and the Mormons.

Much of the Apostle's Creed is setting a precedent for the divinity of Christ....there were heretical sects that either denied the divinity or humanity of Jesus (stating either He was just a man or was never a man to begin with aka a God on earth; those that denied the crucifixion). Much of that is also backing up the historicty of the Biblical events.