I’m a firm believer that the creators of LOST didn’t have a real idea where the show was going until mid-third season, so I’m not even going to try and defend the “open-endedness” of so many mysteries. That said, here’s what I think they were trying to say in the finale, which wraps up the show nicely:
We live on this island together, a place filled with unsolvable mysteries and utter chaos, unexpected enemies and friends—but in the end, the island isn’t what matters. What matters is the relationships we create, for in the end, they are all that we take with us.