Bok captain Kolisi suffered a serious knee injury in April, casting major doubt over his availability for the team's title defence, but he has been selected for the first time this year against Wales in a warm-up fixture in Cardiff on Saturday.
"It's massive for us as a team to have Siya back in the mix," Kolbe told reporters on Wednesday.
"The way he has set his mind to return to play and focus on his rehab, putting in the extra hours with the physios, shows what type of person he is and what this team means to him.
"He means a lot to us as players with his experience and the energy he brings. Even when he was not playing, he was on the sidelines giving input, helping a lot of the guys."
The Boks may not be favourites in many people's eyes to claim back-to-back World Cup wins, but Kolbe says that in many ways, they are better equipped for victory than four years ago.
"We have got much more depth in the squad than 2019. It is actually scary. If someone gets injured, we know the next guy coming in will fill that role and is capable of doing even better.
"The nice thing about this team is that no one is bigger than the next person and whoever gets the opportunity to play, we encourage that person to give him confidence and make sure he is well-prepared."
FIRM FRIENDS
Kolbe will be up against Wales flyhalf Dan Biggar, with whom he had a memorable stand-off when the Boks beat the Welsh 32-29 in Pretoria last year.
But since then, they have become firm friends after playing together at French side Toulon last season.
"I spoke to him when we arrived (in Cardiff). We are friends, he is a good guy, but when the weekend comes, we know what we need to do for our respective countries," Kolbe said.
"He is a competitor on the field and a guy you like to have on your side. He gets under the skin of the referee. He is a wonderful player and has a lot of experience."
