Is Christianity the sum of the actions and beliefs of its adherents or a set of actions and beliefs defined by the Bible?

Mike Horton has in the past year (2011) has frequently defined Christianity as God's acting on our lives and integrating us into His story of redemption. I realize this isn't one of the choices you gave, but I think this is the right way to view the Christian scriptures. If it is our actions, then we have a long history of failure. If it is actions described by the Bible, then we are constantly failing at it and Christianity is an impossible theoretical religion. If it is God's work in saving a people for Himself as described in the Bible, then we can begin to talk about the religion.

Bug now, thus says the Lord, your Creator, O Jacob, And He who formed you, O Israel, "Do not fear , for I have redeemed you; I have called you by name; you are Mine!" [Isaiah 43:1b]

That is your God, and that is your religion: His action.

Hope that helps.

Both. "Christianity" as a concept has fuzzy boundaries, and both the Bible and the adherents appear important to its nature, and so it seems most apt to meld both into one set and state that the religion(s) of Christianity corresponds to this set in some way(s). To try to define it more formally than that doesn't buy any clarity and isn't rooted in anything objective.

Yes.

I'd have to chalk that us as a false dichotomy because:

Christianity is a personal encounter with the person of Jesus Christ.

Being Christian is not the result of an ethical choice or a lofty idea, but the encounter with an event, a person, which gives life a new horizon and a decisive direction.

Pope Benedict XVI, Deus Caritas Est

The Church as a spiritual thing would exist without any members. Each person adds his or her talents to the Body of Christ. It is not a black hole, but as Lewis and Chesterton both allude, it is something that is bigger on the inside than it is on the outside. It is supernatural, the Bible is evidence of the real covenants which God has made with His people, be they Jews, Muslims or Christians. However, no new covenants will be made because the eternal one was as good as it gets.

Take this, all of you, and drink from it: for this is the chalice of my Blood, the Blood of the new and eternal covenant; which will be poured out for you and for many for the forgiveness of sins. Do this in memory of me.

From Eucharistic Prayer 1

This question is very subjective as it appears you are trying to separate what Christianity is from what its adherents do, and that is very tricky.

Jesus had a vision of God's message that he understood very well. Then he gave the pieces of the mosaic to his apostles, and taught some parts to his disciples.

They then tried to recreate the picture that Jesus understood.

So, they passed those pieces on to use in the form of writings, but many of these came from disciples of those Jesus taught.

So, we now have thousands of different groups each claiming to have reconstructed the picture, but each one is very different, as some will have put different ones in the center, and most will have some pieces left out of the image as unneeded.

So, when you ask what is Christianity, both can be seen as Christianity, there are the teachings, but how those are applied in the real-world shows whether the teachings are reasonable to follow, and so likely to be true. If you teach a belief that no one can follow at all, then it is probably not a true teaching, but just a theory on how to live life.

So, in the US, we have Christian groups that teach hatred, and teach that treating those not of their particular faith as being less important, unless they can be converted.

This would seem to fly in the face of Jesus' teachings of loving enemies more than ourselves (not something Jesus stated directly, but can be inferred), and being willing to die for those that persecute us. But, these followers can seem to be happy with making this unreasonable loving part less important, or redefining it.

But, to an outsider, this is Christianity. To those on the inside they may state it isn't, but if anyone group claims to be Christian then the entire teachings of Christ are judged by the actions of the claimants.

This is why Fulton Sheen stated that people don't hate Roman Catholicism, they hate what they think Roman Catholicism is. People see something and may misinterpret, and so they hate this religion because of what they see, and what they may misunderstand, but to those within the Church they will see it differently and so not understand why people will judge the religion so harshly. I am not trying to defend the RCC, but to use it as an example, btw.