The display of true Christianity is revealed in a few ways throughout Romans 12.
Christians are to love genuinely (9a)
Christians are to pursue holiness relentlessly (9b)
Christians are to enjoy familial affection for one another (10a)
In this episode, we see that is also displayed in service. True Christian service is marked by passion, not apathy. It is marked by diligence, not laziness. Why must this be true? These characterize the believer's service because this service is unto the Lord!
