What Blackbeard's speech meant.

Bellamy was lambasting Luffy for believing in something fantastical because he himself believed in Doflamingo's idea of a New Era. This New Era would be one where pirates would simply be organized crime. No adventuring to find new lands or exploring new places to be free, but absolute pragmatism and capitalism.

Blackbeard opposes this because he does not believe that human greed will ever be satiated. The day when people go out to sea to seek the impossible will never end. Adventure and the promise of treasure will always drive humanity. Of course, Blackbeard is focusing on the latter. This does not gel with Luffy, who believes in adventure.

And this is of course brought back in Egghead. York and Vegapunk are the two sides of this coin. Blackbeard will continue to aim for the top.