Sand and Treat Deck Railing?

OK. I'm back for my second novice inquiry. We've got a nice deck out back but the fellow who own ed the house before us never finished the railing/spindles, etc. I am guessing that it needs a good sanding and then....what?

Can someone give me a little guidance here? After I get it sanded, is there a treatment I can put on it to salvage it? I can't afford the time or money to redo the entire thing and I don't think I need to. I just want it to stop deteriorating, and I want to save someone from a handful of splinters.

I am hoping that is a spray on something that will do the trick? What's the best thing for me to use and the best way (easiest) way to apply it?

Thanks!

~dan