The reference is to the story of Gideon from the book of Judges. The story begins with Gideon threshing wheat while hiding in a wine press. The Angel of the Lord appears and says to him, "Hail mighty warrior! The Lord is with you." The Hebrew is from that passage. The image is one of Gideon's request to God to have a fleece wet with dew and the ground dry so Gideon could know that God is with him and will protect him against the Midianites. I'm a bit of a Bible geek (well just a geek in general), so most of my beer labels so far have had biblical themes.
Edit: I forgot to add the reference if you're interested. It's from Judges 6:12