Moreover, God is able to make every grace abundant for you, so that in all things, always having all you need, you may have an abundance for every good work.
That's pretty awesome, as the young priests say. Every grace, abundant, in all things, always having all you need, an abundance of grace for every good work. What more could you need?
Well, it couldn't hurt to notice the introductory verb: God "is able to make" these graces abundant. This verse is a dogmatic statement on which we have to place our faith that, in our particular case, He will make them abundant.
The context of the verse is also noteworthy: St. Paul is encouraging the Corinthians to keep their earlier promise to send a generous donation to the poor Christians of Jerusalem. That is, they have already begun a good work, and he is urging them to complete it, in faith that God will provide them with everything they need.
In other words, those abundant graces St. Paul is writing about aren't merely poured out willy nilly. They are poured out in order to support and sustain us in our own good works.*
The wonderful promise of 2 Cor 9:8, then, is not a promise of prosperity; the grace is free, but not cheap, and we receive it not as heirs but as stewards.
* There are other abundant graces poured out that start us on our good works, and even other graces poured out on the just and unjust alike. But that's not what St. Paul is referring to here.