What does Judges 7:4 mean?

But the Lord said to Gideon, There are still too many. Take them down to the water, and I'll sort them out for you there. If I say, 'This one will go with you,' he goes. If I say, 'This one won't,' he doesn't. Judges 7:4 - Modern Text Bible

(God wants to reduce the army even more, so he gives Gideon a way to separate the men.)