Arsene Wenger's men have lost just two of their 15 matches in all competitions so far this season, with their latest 2-0 success at Crystal Palace last weekend helping them stay top of the Premier League.
Mertesacker thinks that facing Chelsea, Liverpool, Borussia Dortmund and Manchester United in the space of 11 days will provide a perfect acid test of Arsenal's recent improvement.
He told The Mirror: "The games we have coming up will be the test. We know we have started well this time.
"When you compare this to the last three seasons we are in a better position and it feels much better to be where we are now. We are not behind and don't have to get anything back which gives us more safety.
"We are in a strong position and we want to keep that. But that is going to be difficult."
The German international has been virtually ever-present at the heart of Arsenal's defence this season, forming a centre-back partnership with Laurent Koscielny.