"Yes, although I have seen most of the races that frequent the void, I have never heard of anything with Hell-Fire. That is what made me spare you all those years ago. I did not create you and therefore it was allowed that I let you inhabit the world that is rightfully yours." Ra decided to tell him that he spared him instead of the actual truth. 3000 years ago he saw that egg and actually did try to destroy it, but was unable to. Instead of showing weakness, he went back and told the other Gods that he had spared him because he was not actually his created race. The Gods eventually agreed on it, but he kept the little fact that he was unable to destroy it his little secret.