When applying the finish to a bowed psaltery, it can go a lot faster if you can do both the front and the back at the same time. Ordinarily, with a psaltery being two-sided, you’d have to finish one side, let the finish harden, and then finish the other side.
What these pins do is act as a standoff for the rest of the instrument, so the finished top doesn’t touch any part of the table. From here you can proceed to finish the back and sides.