If your audience is on Facebook, then yes, that's where you will link your landing page. Make sure to warm the audience. You can start doing so right away. Let them know the benefits of your freebie (not familiar with devotionals, but address why your readers would want it in their lives, and how it will improve their lifestyle, or something along the line.)
Start posting content around your devotional so that by the time Jan 3 rolls around, your audience is already familiar with your freebie to an extent and are anxiously waiting for it.
And then, on Jan 3, share the link to the landing page and see your list grow!