Wood Finishes and Humidity Changes

Does finishing wood help prevent it from taking on moisture from the air?

You bet!

But it won’t completely eliminate this transfer, so in the long term, adding a finish can only slow the process, and minimize the effects brough about by seasonal changes, but it cannot completely prevent wood from taking in moisture from the air. (i.e., if you move to a desert with a consistent 10% relative humidity, eventually the wood will reach its Equilibrium Moisture Content, or EMC)