It took Luke two whole days to finally accept what has happened to him. In the beginning, he thought he was having a very long dream that was happening before his death, actually, he still was thinking that was what's happening, but now he had a different view. Be it a reality or a dream, this was his chance to change things to what he wants. This was his chance to face destiny and control his fate.
The first thing he needed to do to control his fate was get more power, and more influence. The demons weren't going to do anything for the next three years. Within those three years, something would trigger the demons and would later spark the war. As a nobody, Luke wasn't privy to any information about why the demons started their invasion. Of course many voiced that the demons attacked simply because they were demons. But of course, there were also other voices saying it was a certain human's fault.