1 Corinthians 7:31
And they that use this world, as not abusing [it]: for the fashion of this world passeth away.
Note 11 at 1Co 7:31: All of us have to be occupied with the affairs of this world to a degree. We have to make a living, eat, take care of our bodies, etc., but we should always remember that all these physical things are only temporary. It is only the spiritual things that we accomplish that are eternal.