It seems to me as if this passage encourages one to do whatever one does, solely for oneself. Even as it claims serving humanity to be a worthwhile pursuit, again: so that it benefits oneself. It is unfortunate that spirituality is so universally misunderstood. True spirituality involves the service of God, exclusively for the glory of God, as opposed to being able to get something out of doing it, for oneself.
True. Any act of service done with a motive to receive something back for oneself is not a true service. It is a business. Real service is done with complete selflessness. Thanks The Crow.