Flamini was brought back to the club on a free transfer after he left AC Milan in the summer, and the Frenchman has been sensational for the Gunners since making his return.
"I admit I hesitated. I don't usually let that happen. With me, once they leave, they leave," said Wenger.
"But he has given us a balance between attacking and defending.
"He is also somebody who accepts what I consider to be the dark role in the team. You need that for the balance of the team.
"It was there before but at times on big occasions we seemed afraid defensively.
"He gives us something more on that front. The future will decide if he becomes an important signing - but I was hesitating about it."
29-year-old Flamini admits it feels like he has never been away from the club, he left in 2008.
"I have the sensation I never left. I am happy, enjoying life. It was a great opportunity to come back," he said.
"I had some unfinished business. I had four great years, amazing memories, but I have some regrets.
"I am talking obviously about the Champions League Final in 2006 in Paris which we lost and maybe the 2007-8 run, when we were top of the league and we collapsed in the end.
"All these things stay in the back of your mind. When you are a competitor you wake up in the morning and you want to win.
"You want to win every game. You want to win titles. That's what you fight for. So I come back with a lot of motivation.
"I had some good times in Milan, winning a Scudetto. I missed the Premier League a bit so it is good to be back. I missed the game - fast, physical, with a lot of space, open, with lots of goals.
"There is not much difference now from when I left. The same coach is here with the same philosophy, so that's already important to have stability. So maybe that's why it is so easy for me to be part of the team. I really have the sensation I never left.
"We have a lot of qualities, we have proved that in the games until now. But I don't want to say anything. I have heard people around talking about Manchester City, United and Chelsea but Arsenal is a big club, so of course we are part of that group aiming to fight for the title.
"The championship is a marathon not a sprint. If we can create a surprise at the end, why not? Team spirit is very difficult to find and very difficult to keep, so we have to work very hard on that because for me that is what makes the difference.
"The early criticism of the manager? That's football. Football moves quickly in one way or another. Arsenal had a difficult period but the manager never changed his philosophy and believed very strongly in this team.
"I'm really happy he has proved what he did was the right thing.
"I just feel very lucky to do what I do. I wake up every morning and play football, my passion - and I am paid for it. I am enjoying every moment.
"Sometimes it is difficult to realise how lucky we are. When we have young guys coming in the team we tell them to focus, work hard but also to enjoy it, because you have the chance to play in front of 60,000 people."