Luther said that in Philemon, Paul is “playing Christ in the drama.” The drama of Philemon is the drama of reconciliation; not merely between Philemon and Onesimus, but reconciliation within the koinonia of the body. The church is constantly bombarded by those who would pursue its fragmentation. But as N.T. Wright observed:
But there will always be forces that try to tear the church apart. But there will always be the gospel itself to point the way—of humility, forgiveness and reconciliation—by which unity can be not only precariously preserved but solidly established.
The answer to disunity is and forever will be the gospel of grace, which is reconciliation.
Resurrectio et Vita 
This unity of the gospel of grace is proclaimed in paedocommunion. For most, that means reconciliation begins with I Corinthians.