Greg Tidwell wrote recently in an article titled, “The Open Door” (link is a PDF file):
The church in Philadelphia demonstrated faith in the word of the Lord and faithfulness in the conduct of their lives. What was the reward for their faithful service? Jesus gave them opportunity for more service. He gave them an open door. This example illustrates the point Jesus often made, the one who has will be given more (cf. Luke19:26, Mark 4:25).
The more you serve the Lord, the more opportunities for service you will find. But, remember, an open door is an invitation to service, a starting point rather than the finish line.