All of the religions other than Christianity that I have studied boil down to a system that relies on people's own merit, i.e. do the right things and you'll go to heaven, paradise, nirvana, etc. Christianity is the only religion I've found that pivots not on personal goodness, but grace: I'll never be good enough to get into heaven, but because God loves me he has made a bridge through grace. If you see truth as something empirical, that either is or isn't, the very uniqueness of this concept should be a clue to its accuracy. In other words, if A, B, C, and D are all saying the same thing but E is saying something different, that difference lends weight to E's message, because the others cannot claim to be the true path if they are essentially the same, particularly when some of them claim exclusivity.
There are other things that support Christianity--the variety, complexity and simultaneous order of creation (including us!), the moral code that is virtually universal among human societies, among others--but ultimately, God did not leave absolute evidence of his existence for a reason: he wants us to seek him and love him of our own free will, not because we have to accept him as we accept the physical world around us. (If you wonder, "why not?" just think how unfulfilling it would be to have someone love you only because you cast a spell on them. In your heart, you would know that could never be real love.) He has left ample clues, but he will not force us to draw conclusions from them. That's the point of faith.
To briefly address your point about forgiveness, we have to remember that when we sin it is not only other people we have injured, but most of all God. After all, we might be able to reason that others deserve our actions to repay them for how they have wronged us, but how can we ever justify hurting God, who has given us every good thing we have and life itself? This is why some reconciliation, some payment had to be made for the debt of our sins. You have probably already read other descriptions of the concept of sacrifices; this was not unique to Judaism, but is found in many religions, though the sacrificial objects differed. This is from where the concept of blood debt derived. Even outside the realm of spirituality, the idea of owing a debt for one's wrongdoing is found in every government's justice system. Both the sacrifices and prison sentences provide a limited amount of restitution for a specific act or time period; conversely, Christ's sacrifice pays the debt of each person in full, because unlike the other sacrifices which were worth less, he was perfect. If you need an analogy, visualize that you're taking a shortcut across some train tracks after the warning gate has come down. You are startled by the horn of the train that suddenly appears and trip, but before the train hits you, someone shoves you off the tracks. By the time you turn around to see your savior, you see him, thrown 30 feet from the tracks. Knowing that you deserved to be hit by the train but were rescued, you have two choices: you can either live your life as though nothing had happened, or you can let this be an opportunity to live in a way that honors that sacrifice. I hope this gets you a little closer to the truth you seek.