Philippians 2:22
As a son with the father, he hath served with me in the gospel.
Timothy had been a great help to the Apostle Paul, serving with him in his gospel outreach. A work for the Lord can be done in conjunction with others, helping them in their service for Christ. We all need to be especially concerned that we are doing what the Lord wants us to do, and, above all, that we are doing it from a willing heart.