Perceiving Impact is a Powerful Motivator

From Give and Take by Adam Grant:

Along with reducing burnout among givers, a firsthand connection to impact can tilt people of all reciprocity styles in the giver direction. When people know how their work makes a difference, they feel energized to contribute more. 

If you have employees, ensure they see how their work impacts people. An easy way to do this is to have them meet customers and potential customers. Have them take some support calls, and walk on the sales floor.