#1 Unbeatable legacy

Lionel Messi has already achieved EVERYTHING there is to achieve at Barcelona. Be it the highest goalscorer in the history of the club or all the club trophies available, he has won it all. And now what’s left is creating a legacy that can never be beaten by anyone else.
And it is really possible for him to do that.
For starters, he needs to overtake Xavi Hernandez as the player with most appearances for the club. Right now, he sits at number 3 behind Andres Iniesta and the aforementioned Xavi. Xavi played a total 767 games during his time at Barca and Messi is currently at 602.
If he fulfils this contract, then there is little doubt that he will overtake that record and given the way he scores, it might not be an exaggeration to claim that he will get at least another 150 goals in the next 4 years – taking his tally to 673 by the end of his Barca career.
And there will be some more trophies along the way, which would make his legacy almost unbeatable. Perhaps, definitely unbeatable.
And this factor alone makes it a great decision for him to stay at Barca.