David Luiz said he left Chelsea to join Arsenal because of his "ambition" and to experience a "new challenge".
The 32-year-old centre-half made his Gunners debut in Saturday's 2-1 Premier League home win over Burnley after his move on transfer deadline day.
Chelsea, who beat Arsenal in the Europa League final, came third in the league last season with Arsenal fifth.
"I am a guy with ambition and that is why I moved. I like a new a challenge and new things in my life," said Luiz.