The Gunners paid £8m to sign the Brazilian defender from local rivals Chelsea.
Speaking to the club’s website, Luiz said: “It’s a big club – not just in England, but everybody around the world knows how big Arsenal is.
“When I had an opportunity to come to this kind of big club, I had to take it. That’s why I’m here.
Asked about his decision to switch London clubs, Luiz added: “The cycle finished there. It was a conversation between me and Chelsea and everybody. I had an opportunity to come to another big club. In my life, I’ve always liked to do some challenges. I’m not scared at all to try things.
“I think not too many players would make this kind of move, they would maybe be scared, or something like that. I’m just trying to do big things in my life, so like I said, my cycle at Chelsea finished and now I’m excited to start a new chapter in my career.”