Like all the previous "Memories" episodes for this series, all this is is a recap episode but with Luminus/Luminous narrating the events this time. That's it. It's just a recap episode. Same scenes from the anime, same backstories that has already been explained. You're not missing out on anything that you wouldn't already get from just watching the show. Normally I'd just recommend watching the series again (at least up until episode 11 which is where this recap ends) if you want a refresher but this season has a lot of drawn-out meetings for about 1/3rd of its run so... maybe this might be useful for you?