It's not 100 per cent clear how to get to the final credits in the excellent new PS4 game God of War, and you may think that you'll have to finish all of the side missions first, but that is in fact not the case. Here's a spoiler-free explanation.
Once you've completed the game's story, you'll be put back in the open world and encouraged to go fight, explore, and do all the side stuff you haven't finished yet. It may seem like something's missing, and that's because you're not quite done yet. To see the final ending, you have to do the following:
1) Go back to Kratos and Atreus's home (you can use the Mystic Gateway).
2) Go to sleep.
That's it! Then you'll see one more scene and the full credits will roll. Once they're over, you can go back to side quests, optional bosses, and throwing the axe and calling it back over and over again for 40+ hours at a time.