“Perhaps the reason he was separated from you for a little while was that you might have him back forever—no longer as a slave, but better than a slave, as a dear brother.” Philemon 1:15-16
Onesimus was a slave under the authority of Philemon. He was given to Paul while in prison at Rome. Onesimus was a dear friend and comforter for Paul and became converted to Christ.

At one time, Onesimus was a useless person but when he became a believer he became very useful.
Paul is sending Onesimus back to Philemon as a free man even though he may continue to do the work of a slave. He is now a believer and a dear brother in Christ. He is free from the bondage of the world and is now a slave for Christ.
Onesimus is above all reproach and has been covered by the blood of Christ for all his sins. He has to be accepted without stigma or disrespect. He is as worthy as any believer in the world.
The point of this story is the moment you make a decision for Christ you are set free from all bondage and immoral living.
You are a new creature in Christ Jesus dedicated to live for Him and are no longer a slave to anything in the world. Now you are a slave seeking the will of Christ.
Onesimus now has the scruples of Christ living within him through the Holy Spirit. This causes him to hesitate and turn away from sinful actions.
The transformation of Onesimus was a change from having little utility in Christ to becoming a disciple of Christ filled with the power of the Holy Spirit.
Onesimus is now a vessel of God spreading light to those living in darkness!