How do you defend Christianity against Agnosticism?

Answer 1

Agnosticism does not attack Christianity; if anything, much the opposite.

The agnostic position is simply "there is no conclusive evidence that proves or disproves God" - they might think there is despite the lack, they might think there isn't because of the lack.

Many agnostic theists are in fact Christians. Hence, there is nothing to defend against.

Alternative Answer

I am agnostic, and you're probably looking for a way to put across to the person that Christianity is correct. An agnostic can only say why he is not a Christian in terms of Atheistic beliefs, so he might say that he does not know whether God created the world because of Big Bang theory. Therefore what you are defending against is and can only be Atheism. Therefore you could read one of many books to find the answer. In order to defend, your knowledge must be comprehensive, so it is no good me telling you defences against such theories, as they can just come up with more atheistic beliefs.

The core belief of Agnosticism is not one which opposes any religion. The only defence you need give is your faith. An agnostic who does not know God should understand that for ones self, faith is evidence enough that God exists, and this is how you 'know' that God exists. Therefore, you only need to attack their beliefs. Agnosticism is based on uncertainty, yet nothing is certain. Even the most basic mathematical proofs, I am told, are not certain. 1 does not, apparently, have to equal 1. Therefore, what is certain? You must have faith in one thing to know anything, for all belief systems must have a fundamental belief, which is held as fact, but requires faith. If one does not know if anything is for certain, there is no reason to live, as the truth can only be revealed after death. Yet if they have chosen wrongly and have not followed God, they will suffer in Hell forever, which keeps them alive. Surely by this logic, the only way to find the meaning of life is to have faith? What this faith is in is up to them, but they are unlikely, having been agnostic for some time, to be an atheist at the end as they are likely to always have the nagging feeling that God might exist. The only way out is Christianity.*

I hope this has helped. I always, contrary to the above answer, debate religion, which involves 'attacking' it. However, at the end of the day, both arguments do, to some extent, cover all topics. All unknown is explained by "God knows" or "We will find out, by science", and thus both are comprehensive...

Pick a side.

*By this I re-emphasise that they are unlikely going to be able to break the habit of uncertainty, but if they find faith, they will have no need for uncertainty. Therefore an agnostic who becomes an atheist is unlikely to truly be an atheist as they still doubt the certainty that there is no God.