"whatsoever ye do, work heartily, as unto the Lord, and not unto men; knowing that from the Lord ye shall receive the recompense of the inheritance: ye serve the Lord Christ." (ASV)
Have you ever spent time with a real complainer? Someone who never has anything good to say and can find the bad in any situation? It can be a difficult experience. A pessimist can bring down even the sunniest disposition if we're not careful. Negativity has a way of infecting those around them.
At one time or another we've all complained about our job. Maybe our work is stressful, our boss doesn't appreciate us, or we don't get along well with our coworkers. Paul gives us an important reminder. We aren't working for our boss, our company, or our coworkers.
"We are ambassadors therefore on behalf of Christ," (2 Corinthians 5:20 ASV) Our main job as Christians is usually not the one that pays the bills. That is important too, but it's secondary to the work we are called to do as disciples of Christ Jesus. In reality, we Christians are ambassadors for God's kingdom, and in everything we do, we are working for Him.