I would suggest a coat of Sanding Sealer, smooth it down with 240 then 320 Grit, then Varnish it. If you don't have any Sanding Sealer dilute the first coat with White Spirit, 2 parts varnish and 1 part White Spirit. Sand down as above then 1 or 2 top coats. Don't put neat Varnish straight onto bare wood, you'll never get it smooth.
John