What does this statement by Eumaeus mean, "Servants never do their work when their master's hand is no longer over them, for Zeus takes half the goodness out of a man when he makes a slave of him."?

Eumaeus is the loyal shepherd for Odysseus; he notes that servants need the guidance of a master to do their work well. He hints that if there is no guidance by a master, there will be subjection to the will of the gods almost as if the master intervenes between the gods and the servant. Since servant and slave can be almost the same, Eumaeus is suggesting that working with a master is like being a servant while working with/for the gods would be like slavery.