As he recovers from an ankle injury that has sidelined him since February, the 27-year-old admits that the initial transition was difficult.
"Sometimes I felt like it was very hard, especially when I first came here," Mertesacker told Arsenal Player.
"It was tough to settle down [and I was] very quickly into the first squad. There was sometimes a lack of performance but I think you have to go through that to improve yourself.
"I am very comfortable here now, and very proud to be with this Club."