If you would have to choose one single core tenet of Christianity, the most important one, Christians would often choose "Jesus died for our sins" (or something to that effect.)
My answer to that? "No, he didn't."
One of the basic tenets and core beliefs of Christianity is that Jesus is not dead, he is alive and well, and even has his own human body (albeit in some kind of ascended form.)
What exactly did Jesus give up in order to "save" us? What was the great loss? What was the great price that he had to pay? Absolutely nothing. And this is not me saying that. It's what Christianity itself teaches.
And that's not even going into the crazy reason why he had to suffer and die, which makes no sense whatsoever. Just the mere fact that Jesus did not, in fact, have to pay anything at all to "save" us is nonsensical in itself.
Some could argue that the suffering itself was the price. Even setting aside that it makes no sense, Jesus himself knew that the suffering would be temporary and that he would be just fine afterwards.
It would actually make more sense if Jesus had been sent to Hell for all eternity, to suffer for our sins there. Then it would have been a true loss: God would have lost his own son, God would have had to give up part of his very self, to suffer indescribable torment and agony for all eternity, with absolutely no possibility of return or end of the suffering.
The story and the theology would actually make more sense that way. That way there would at least be some rationale behind the sacrifice.
(Naturally this wouldn't solve any of the other problems that still exist with Christian theology, such as why did God create Hell in the first place, or why does he send his own creation there to suffer for eternity, and how he can be so cruel. But at least this way Christian theology would be at least slightly less nonsensical.)