#1. Bobby Lashley was added to give Big E the biggest win of his career
The biggest wins of Big E's career might be the Money in the Bank 2021 as well as his cash-in on Bobby Lashley to become the WWE Champion. So far, his title reign has been good and quite different from Lashley's, primarily because one is a babyface and the other is a top heel.
Either way, Big E hasn't had a defining WWE title victory since he became champion. Perhaps the best match he has had since his title win has been against Bobby Lashley's biggest 2021 opponent, Drew McIntyre.
Apart from the McIntyre match, E needs a big victory to define his title reign. Adding Lashley to the mix not only adds a great deal of star power, but it will add a great deal of legitimacy to Big E if he walks out victoriously at the Day 1 pay-per-view.
Bobby Lashley's addition to the match may simply be to enhance the New Day member's status as the WWE Champion - even if he isn't taking the pinfall.