Tail thread to close edge stitches?

I’m finishing my first shawl (Leaf and Lotus), and I’m really confused. At the beginning, I was instructed to do a provisional cast-on, which I did. The pattern then said “the tail thread will be used later to close the edge stitches.” I thought at the end it would explain how this is done, but alas. I’ve tried googling it, but I can’t find anything that explains this. Does anyone know what this means and how to do it? Thank you!

It looks like there is a small gap at the center on the flat edge of the shawl. Is this where your yarn tail is? If so you can probably use the tail to close the gap just as you would to begin mattress stitch or to close a gap at the beginning of a hat in the round. Take a sewing stitch or two across the gap to snug it up.

Yes! Right now, there are 15 live stitches in the middle of the straight edge.
I’ll try that, thank you!

Hmm, that’s more than I was imagining. Could you bind them off using the tail of yarn? or maybe graft them together? This project shows the provisional cast on.

If these are the sts from the provisional cast on I’m wondering why the designer has you work the provisional in the first place. No instructions at all for dealing with the cast on sts in the end? It’s worth writing to the designer and to one of the project knitters to ask how to deal with the cast on.

Based on these two photos from the Ravelry project page one could graft or kitchener stitch the provisional edge together using the tail.