The passage
      v9. Paul lists a number of general exhortations: We are to love our brothers and sisters in the sense of show compassion toward them. Such love must be genuine and not deceitful. We are to oppose what is morally wrong and support what is morally good.
      v10. We are to show affectionate kindness to our brothers and sisters in Christ, particularly when they are in need, for Jesus is with them. A kindness to a brother is a kindness to Christ.
      v11. With respect to our service toward God, be dedicated; with respect to our relationship with the Holy Spirit, bubble over with enthusiasm; with respect to our relationship with the Lord, be devoted in service.
      v12. With respect to our hope of eternity, be joyful; With respect to persecution, be patient, and with respect to prayer, be constant.
      v13. With respect to the needs of the Christian brotherhood, be generous. Offer practical care for brothers and sisters in need, and offer hospitality to visiting believers.
      v14. Blessing our persecutors reminds us of the words of Jesus, Matt.5:44, Lk.6:27.
      v15. We must be willing to stand with those around us in their times of trouble. These words may refer to empathy within the Christian fellowship, but there is no reason why they can't apply to the world at large.
      v16. To "live in harmony with one another" probably means "agree together, one with another"; "be of the same mind." This exhortation calls on believers to work at unity in the brotherhood, but also possibly encourages "community" with all our neighbors. Paul also denounces snobbery, encouraging us to be willing to associate with people from a lower social stratum. Also, he makes the point that it is dangerous to think too highly of our intellectual ability. "I think and therefore it is true" (rather than "I think and therefore I am"), is a disastrous assumption.
      v17. Do not return evil for evil. This exhortation on vengeance is oft repeated in the Bible, even by Jesus, Mt.5:38f, Lk.6:29, 35. Paul goes on to encourage right behavior; "let your aims be such as all men count honourable", NEB.
      v18. Where possible, be peaceably disposed toward everybody.
      v19. Retaliation, in the face of hurt and offence, is a natural response. Paul affirms the standard Biblical line, leave the matter in God's hands.
      v20. Proverbs 25:21-22a calls for a positive response to a hurt that may prompt repentance in the sight of God. Yet, we need to remember that a kindness to an enemy does not inevitably make them a friend; it often makes them a greater enemy.
      v21. We overcome evil with good when we respond to a hurt in love rather than vindictiveness. In so doing we defeat evil, as Christ defeated evil on the cross.

Let love be sincere
      The apostle begins his exhortation on practical ethics with the words "love must be sincere." Calvin says of this verse, "it is difficult to express how ingenious almost all men are in counterfeiting a love which they do not really possess. They deceive not only others, but also themselves, while they persuade themselves that they have a true love for those whom they not only treat with neglect, but also in fact reject."
      Any exhortation on personal morality must focus on the heart. It's one thing practicing "brotherly love", "sharing with God's people", "practicing hospitality", not taking "revenge", etc.... but what of the condition of the heart? Paul says, "love must be sincere." When it comes to Christian ethics, the deed cannot be separated from the motive. In ancient Rome the motive was reciprocal - do unto others so that they will do it unto you. In Christian ethics it is "do unto others as you would have them do unto you." The deed of love has worth in itself when it is free from the need of reward.
      Of course, Calvin addresses an even deeper level of corruption when he speaks of deeds of love done to veil a heartfelt hate. When we want the acceptance of others, or even the acceptance of God, we are easily tempted to unknowingly veil our hate (our dislike, disdain....) in deeds of love. Release from this soul-destroying condition is actually quite simple. God's acceptance is freely ours in Jesus. When we hold onto Jesus we are 100% accepted in God's sight. If we can accept ourselves as God accepts us, we will not be very worried about the acceptance of others. We are then free from the need to veil our less presentable motives.
      A sincere heart is not a difficult one to attain. We simple take on the mind of Christ by looking to his renewing Spirit.