Christian was thankful to God that he didn't come to save his mate when she was already dead. Of course, that would mean that he had to ascend to heaven, but he couldn't just deal with the fact that his mate was hurting and he chose to let her die.
He just couldn't do it. For the moment he saved Katrina, he didn't think of her as the woman who betrayed him in heaven but as someone who he should save rather than let her die. When they arrived at the building, he saw red when he saw her bloody and assaulted. A Christian attacked the man who had manhandled his mate in fury, and he didn't regret it.