First, a disclaimer: For the sake of argument, I will be assuming that Christianity is basically true—there is a God, and Jesus actually existed on earth, and the Bible accurately quotes Jesus, etc, etc. And I will use language as such, but my personal views are, of course, that it Christianity is mostly made up stories, just like any other religion.
The first place one should start is with Christian theology, which I find to be nothing more than a theology of convenience. By which I mean apologists make up excuses and then use those excuses whenever they find them convenient and then forget about those excuses when they would be inconvenient.
On the right is a graphic from page 351 of the book, "I Don't Have Enough Faith to Be an Atheist." Below is a quote from the book in which they use an example of what I consider to be theology of convenience (personal additions in RED):
The second and third objections to Christ's deity have to do with Jesus being subordinate to the Father and limited in knowledge. In John 14:28, Jesus clearly subordinates himself to God by admitting, "The Father is greater than I." And in Matthew 24:36, Jesus claims he doesn't know the date of his own return when he declares, "No one knows about that day or hour, not even the angels in heaven, nor the Son, but only the Father." Now how can Jesus be God if he is subordinate to the Father and is limited in knowledge? — Good question. Now for the theology of convenience!See how convenient that is? Whenever Jesus does something that is un-Godlike, it's just his "human nature!" But, the convenience of this theology is not what I am really here to talk about. I am here to talk about the supposed sacrifice of Jesus, and this theology plays a significant part in why it is a joke.
The answer to both of these objections lies in a proper understanding of the Trinity...
Jesus shares in the one divine nature, but he also has a distinct human nature. Jesus is one "who" with two "what's" (a divine "what" and a human "what")...
How does this help us deal with objections two and three? Well, since Jesus has two natures, whenever you ask a question about him you really have to ask two questions. For example, did Jesus know the time of his second coming? As God, yes; as man, no. Did Jesus know all things? As God, yes; as man, no... Did Jesus get hungry? As God, no; as man, yes. Did Jesus get tired? As God, no; as man, yes. (p350-352)
As for the sacrifice, Christians claim that it was some great act of love, often citing the very popular verse John 3:16 which reads as follows in the NIV translation:
For God so loved the world that he gave his one and only Son, that whoever believes in him shall not perish but have eternal life.But did God really "give" his "one and only Son"? If we treat Jesus as purely human, then yes. And this is where I think the Christian thought processes screw up. If Jesus were just a man, then sure, that would be quite a noble deed to give up your life and pay for our sins so that others can benefit. But, even this speaks much more highly of Jesus than of God. Why, after all, was a sacrifice even necessary? What purpose does it serve? If God is the one calling the shots, couldn't he have figured out a better plan? (At this point, some apologists might point out that God is in a battle with Satan. It's really unclear, though, what Satan has to do with anything related to this. Yes, Jesus spends a couple days in hell down with Satan, but why is this necessary? I have never heard a rhyme or reason given that didn't sound like nothing more than a post hoc rationalization, which is a form of special pleading.) Nothing about Jesus' sacrifice would make God necessarily a loving God.
However, when we go back to Christian theology*, Jesus is more than just human. If Jesus is really God (or a part of God), then what is death to something that is part of the creator of death? It should be no big deal. Or did God create death to be more powerful than him? Same goes for Satan. Spending a couple days in the hell that he himself created (or played a part in the creation) should not really be an issue. And the divine Jesus should have known this, even if the human Jesus did not.
* There are, I understand, some denominations of Christianity that do not believe Jesus is/was divine. They are a minority, though, and I am here to address the majority. Apologies to those Christians.
Let's now go back to the idea that Jesus was paying for our sins. Paying who? God...which he is part of. And who created the concept of sin and determines what is a sin? Again, God, which Jesus is part of. This is why some atheists point out that God sacrificed himself to himself to appease a loophole in the law he created. It is absurd. As I asked earlier, why is the sacrifice even necessary? Why, for example, can't God just change the law? Or even just set things right some other way? If anything, it would seem that God might be a bit of a masochist and tortures himself just for the fun of it.
In summary, the only thing that would have been sacrificed was Jesus' human nature, but nothing happened to his divine nature. As the cartoon above illustrates, what "sacrifice" the divine Jesus went through wasn't anything significant, either. So, I ask Christians who think Jesus is divine, "What sacrifice?"