The "Battle Pass Promise" is a promise for Epic to award five free tiers for Season 3 to those who purchased the Season 2 Battle Pass.
This is a loyalty reward
This takes you up to Tier 6 instantly.
New players will start at tier 1, but it shouldn't take too long to catch up to the other players.
Message reads:
"As a special thanks for buying the Season 2 Battle Pass, you'll start Season 3 off with 5 free tiers."