I don't get it (no orthodox answers).

Why do Christians think the issue of blasphemy is at the heart of the matter? Why is it only blasphemy if you've hardened your heart first? If I say something against the Father or the Son, it's blasphemy, so why do people say it is different from speaking against? If an atheist or a person, no matter their heart, speaks against the Father, it's blasphemy, so why do people say you have to have a heart condition to commit the sin? I have tried to understand it, but I just don't get it.