Apologetics is a concept we're all at least intuitively aware of, but some of those who've made a systematic study of the issue have discovered some key points that virtually cripple doubts about the gospel. I am condensing things quite a bit. There are some profound insights (mostly not my own) in what follows, so please read carefully.

Doubt for the Christian could appear to be largely a function of environment. Isn't it easy to trust God living in a time and place where persecution is light?

But think of the early churches, and the apostles. They lived in a time and place where they were subject to crucifixion and stoning at a moment's notice. Most importantly, they were fully aware of God's promises to provide for them and protect them.

Now knowing full well that God has promised protection, I would have difficulties when loved ones or myself were drug out to be killed. I expect doubt would be nearly overwhelming. These people knew God was able to protect them. They could talk to eyewitnesses even if they hadn't seen miracles first hand themselves.

What torturous doubt would enter my mind, knowing that the Almighty was withholding His protection! But they overcame any such doubts, and refused to abandon their testimony even under torture and penalty of death. What could God's plan have been? If He loved them, how could He allow such things to happen?

God was thinking of us. He gave His Son for us, and he also allowed His followers to suffer (at apparent risk to His reputation) for the sake of those who would live in later times. It is precisely because these people suffered so much and were martyred that we can be absolutely sure they told the truth to the best of their ability.

Nobody knowingly dies for a lie. (I must emphasize 'knowingly', as there have been martyrs for false causes.) Thus WE can be certain that the New Testament was written honestly. Unless those men were somehow deceived, their word is good. This cannot rationally be disputed, and if you think it can I suggest you give the matter a few minutes' consideration.

Now determining whether or not the writers of the New Testament were deceived is best done by reading it, and carefully studying to see if they could have been mistaken. I don't care to copy all the evidence here. I will just point out that they were in very close proximity to the events of which they testify, and the single most important event is the death and resurrection of our Lord.

The reason it's so important is that we have a Living Saviour. Without His death, we'd be in bad shape: the price of our sin would still be due. Without His resurrection, we'd just be worshipping a dead man, with no hope after this life, and no basis for hope during this life.

One often encounters the claim "all religions are the same". Or "how do you know you're right and everyone else is wrong?" I say nothing else matters. I'll follow the Living God. I'll follow the God who loves me enough to see to it that I can justify confidence in the Holy Books that tell me about Him. I don't know of any rivals that even come close.