Messi will sign the deal -- which ties him to Barca until 2021 -- when he returns from his honeymoon in Antigua and Barbuda sometime next week.
Barca were always confident that the Argentine would remain at Camp Nou, but nerves nevertheless permeated the fan base when the club allowed him to move into the final 12 months of his current contract. However, with an agreement now confirmed, the club can rejoice at what should amount to their biggest deal of the summer -- and here's why.
1. He is literally irreplaceable
Barca's announcement of Messi's contract renewal extended well beyond the facts of the agreement.
"Messi is the best player in history," the club said in a statement. "He has led the team to an era of extraordinary success, the likes of which has never been seen in world football."
Whether Messi is the best player in history is certainly up for debate, but Barca would be able to provide a strong argument in his favor. He has helped the club win 30 trophies, including eight La Liga titles and four Champions League crowns. He has also become the top scorer in the club's history (507) and has won the Ballon d'Or a record five times. The club would not have enjoyed the same degree of success throughout the past decade without him.
Even last season -- when Barca finished with only one title, the Copa del Rey -- the results would have been worse had Messi not been around. He directly influenced the outcome of multiple games, including: Valencia away, Sevilla away, Real Sociedad away, Villarreal away, Leganes at home, Atletico Madrid away, Real Madrid away ...
So, how do you replacec -- to use Barca's terms -- the best player in history? You can't.
2. It will encourage others to stay
If Real Madrid's dominant season had football fans fretting that Barca's ship was sinking, those same admirers can find solace in Messi's renewal. As long as he's around, the club will continue to compete for trophies and its best players will want to stay put. Ex-coach Pep Guardiola said as much this week.
"With [Luis Enrique], when they were good, they were almost unbeatable," the Manchester City coach said. "They played really good football. While Leo is there, that will always be the case -- he's the best player I've ever seen."
Barca, then, are not in jeopardy of losing their best players. Neymar, Luis Suarez, Ivan Rakitic, Sergio Busquets and Marc-Andre ter Stegen are among those standouts who have signed new deals in the past year. The only contract still in need of renewing is that of Andres Iniesta, whose term is set to expire next summer.
3. It is reason for other stars to sign
By the same token, players join Barca because they want to play alongside Messi.
The Blaugrana's top target this summer is Marco Verratti. And both Diario Sport and Mundo Deportivo report that one of the main reasons the Paris Saint-Germain midfielder wants to come to the club is to play with Messi.
Verratti won't be the only prospective transfer to harbor similar desires, either. While Messi remains at the peak of his powers, who wouldn't want the chance to witness his genius firsthand?
4. There would have been revolt if they had sold him
Although Josep Maria Bartomeu and his board are two years into a six-year mandate, they are coming under increasing pressure from challengers seeking to usurp their throne. Former presidential candidate Agusti Benedito lodged a vote of no confidence against them in June, and ex-president Joan Laporta has called on them to resign (several times).
Benedito's and Laporta's complaints focus on a number of issues that, by and large, have nothing to do with what actually happens on the pitch: the Neymar transfer saga, the Qatar sponsorship deal, etc.
Despite lingering issues off the pitch, the club's solid play has prevented dissent from becoming widespread. Bartomeu's board was elected on the back of a treble in Luis Enrique's first season, and many supporters were happy to ignore certain problems in exchange for good results. Following an unsuccessful campaign, however, failing to keep hold of Messi would have incurred a tidal wave of criticism.
All of this harks back to comments made by Javier Mascherano in February:"No, the club is bigger than any manager, than any player ... except Leo. That's the reality, and you have to accept it."
5. He has a chance to cement legacy over Ronaldo
For all the superlatives, all the accolades, all the records, all the goals and all the trophies, we still want more. We still want Messi to give us more -- to show us, definitively, why he should be considered the greatest to ever play the game.
Although Messi turned 30 last week, there's no reason to believe a decline is coming. Just look at Cristiano Ronaldo, whose most successful years with Real Madrid have arguably come since he hit the big 3-0.
Messi still has time to win more Champions League titles -- one title in the past six years is not enough, Sport journalist Albert Masnou says -- and time to win more Ballon d'Or awards. Most importantly in the eyes of many fans, he still has time to win a World Cup with Argentina.
Based on the way he ended last season, Messi appears to still have fire in his belly. With his future sorted, he can now focus on further cementing his legacy, both at Camp Nou and in the football world at large. Perhaps only when he's gone will we stop demanding more and fully realise the extent of his accomplishments over the past decade.