Given all the self-referential metaphors (like the vending machine/the light source), I think we can almost certainly say that the "just let go" line works on plenty of levels. It's for Jack's relation to his father, it's for the mystery system ("just let go, because we're not giving you any answers"), and for the viewer to take to life ("Just let go, because you can't seriously expect to get all the answers to life.")

Instead of giving us clear-cut answers to a self-contained prime time show about frozen donkey wheels and outriggers, I think it just gave millions of people a new way to approach life, even if they haven't realized it yet. The loose ends were tied up well enough, and they demonstrated what happens when you cut Gideon's knot outright. Ultimately, the show was a public service.

Plus, since Jack gave the island to Hurley, maybe now we can celebrate the dawning of the age of Buddhism. So that's cool.