The Scottish champions overcame Shakhter Karagandy 3-0 in the second leg of their playoff qualifier on Tuesday night to edge the Kazakhstanis 3-2 on aggregate and Forster is now looking forward to another successful campaign after last season's Round of 16 finish.
"It's obviously a World Cup year and it's crucial to be playing Champions League football, especially at a club with the calibre of Celtic," said Forster who was called up to the England squad ahead of next month's World Cup qualifiers.
"It will be a fantastic opportunity again to test ourselves against the best players in the world, which is something we all want to do.
"It's been a good week, I'll take that. It's been brilliant. It's obviously nice to be in the England set-up again.
"Every season seems to be big and I just need to keep myself going. We had a fantastic year last season.
"We have lost a few players since then but it has been key for us to get in the Champions League again and it keeps everyone moving forward."