The move puts Cumberbatch in the mentor role that was previously occupied by Robert Downey Jr., who played Tony Stark/Iron Man in Spider-Man: Homecoming, and by Samuel L. Jackson in Spider-Man: Far From Home, the latter reprising Nick Fury. The role gives Holland a chance to play opposite seasoned actors, gives Peter Parker a father figure and gives the movies extra star power while also tying them to the greater Marvel Cinematic Universe.
EDIT - Annnnnd I spelled Multiverse wrong in my title, can a mod fix that please? Thank you.