It is important to interpret these verses in the context of the servant situation, although they certainly may have a broader application. It is so easy, in difficult situations, to just go through the motions of doing your job, without any heart in it. But Christians, even in adverse situations, are reminded to fulfill their duty heartily, as to the Lord. When we are in a “survival” mentality, we often think thoughts like, “Who cares anyway?” Paul’s answer was that God cares. And He will reward you according to your faithfulness or lack of it.
Source: "Respecting Authority", Biblical Family Values, Adult Teacher's Insights, p. 12.