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.

v9
      anupokritoV adj. "sincere" - unashamed. "Love is to be the real thing, genuine, and not counterfeit", Cranfield; "don't pretend to love", TH.
      kollwmenoi (kollaw) pas. part. "cling to" - cleaving to, glued to, be joined firmly to. The participle is obviously imperatival, as with "abhorring (hate) the evil". Similar imperatival participles continue through the passage. We must hate the evil, flee from it, but join ourselves to the good, be passionate for the will of God.

v10
      th/ filadelfia (a) dat. "in brotherly love" - with brotherly love. The dative can be understood in numerous ways, eg. Instrumentally "by means of brotherly love", TH; as a dative of respect, "with respect to brotherly love", Morris; dative of manner, "as between bothers", Phillips; dative of advantage, "for the brotherhood", Moffatt. The term "brother" for a fellow adherent of a religious faith, is not peculiar to Christianity, but it was used by Christ and adopted by the first believers.
      filostorgoi (oV) "be devoted to" - love warmly, cherish, be affectionate toward. "Tender affection, particularly family affection", Cranfield.

v11
      th/ spoudh/ (h) dat. "in zeal" - earnestness, diligence, dedication. Again the dative here, as with the two other datives in this verse, may be translated in numerous ways. Possibly again a dative of respect; "with respect to dedication (toward the Lord / the brotherhood?), never be lacking." Possibly a dative of cause as in v12, "in zeal" = "by virtue of", BDF, "on the basis of."
      mh oknhroi adj "never be lacking in" - slothful, lazy, slackness, irked by the demands of (Murray). The adjective here takes a verbal role. Moule regards that here it serves as an imperatival participle, so best translated as a positive imperative to parallel the positive imperatives of this verse and the next; "be constant in zeal." The phrase illustrates the attitude that drives a person to sidestep their responsibilities in favour of as little work as possible. cf. Matt.25:26.
      zeonteV (zew) part. "fervor" - burning or boiling,.... the burning within, fervor. We must be set on fire. "With respect to the human spirit (possibly the Holy Spirit), bubble with enthusiasm", or possibly, "be on fire within."
      douleuonteV (douleuw) part. "serving" - serving as a slave. "With respect to the Lord, be devoted in service." Note the alternate reading "time" = the present time, serve it; "seize your opportunities", Barclay.

v12
      caironteV (cairw) part. "be joyful" - rejoice. The imperatival participles continue.
      th/ elpidi (iV idoV) dat. "in hope" - hope. The dative again leaves us with numerous translation possibilities. Do we continue with "with respect / regard to", or go with a dative of cause; "be joyful in hope, ie. by virtue of hope"; "if you have hope, this will make your cheerful", JB. The grammar indicates a similar approach to v11 and 12, so a dative of respect may be the best all-round option.
      proskarterounteV (proskarterew) part. "faithful" - persevering. "Busy oneself with, be busily engaged in", BAGD. "Faithful" doesn't quite express the "keeping at it" sense, although Paul is not saying that we should keep praying until God gives us what we want. Probably "constant" carries the sense better than "persevere".

v13
      taiV creiaiV (a) dat. "in need" - Probably again a dative of respect, "with regard the needs of the saints, share."
      koinwnounteV (koinwnew) part. "share with" - share. "Contribute a share", BAGD. "Contribute to the needs of God's people", NEB. Poverty was a fairly serious problem for the early church, as it was for the Roman Empire as a whole. Accommodation was also limited and expensive for travelers, so these exhortations meet a very practical need.

v14
      eulogeite (eulogew) imp. "bless" - invoke God's blessing upon (Murray); "call down blessing on", NEB. Note Paul's switch to simple imperatives. Calvin says of this exhortation, "although there is hardly anyone who has made such advance in the law of the Lord that he fulfills this precept, no one can boast that he is the child of God, or glory in the name of a Christian, who has not partially undertaken this course, and does not struggle daily to resist the will to do the opposite."

v15
      cairein (cairw) inf. "rejoice" - to rejoice. The infinitive is most likely imperatival, an uncommon infinitive in the New Testament. "Share the happiness of those who are happy, and the sorrow of those who are sad", Phillips.
      meta cairontwn "with those who rejoice" - with rejoicing. Obviously the participle is functioning here as a noun, even though it is without the article.

v16
      to auto eiV allhlouV fronounteV "live in harmony with one another" - thinking the same to one another. "Treat everyone with equal kindness", JB, but this is not quite the sense, as is the NIV stab. Probably better, "be of the same mind", Morris. Verse 17ff are taken as general exhortations for believers in their contact with non-believers, but v16, even 15 and 14, may not be church specific. Paul is not encouraging us to paper over differences. We are always bound to stand for the truth as we see it.
      sunapagomenoi (sunapagw) part. "associate with" - led, or carried along with. We should not be "carried along" by high-mindedness, but rather by "the humble tasks in community", Black. Christians who think they are socially superior are really not standing with Christ.

v17
      mhdeni "anyone" - no one. Emphatic.part.
      pronooumenoi (pronoew) "be careful" - taking thought, to have regard for, aim at, seek. The exhortation to do what is right in the sight of others is interesting. The NIV sense can easy imply the performance of goodness, but the NEB gets to the heart of it with "let your aims be such as all men count honourable."

v18
      to ex Jumwn "as far as it depends on you" - it from you. "To the extent that it depends on you" Moo. "It" is an accusative of respect, Moule = "so far as it is in your power." Calvin says of this verse, "we are not to strive to attain the favour of men in such a way that we refuse to incur the hatred of any for the sake of Christ." We are to maintain peace as best we can.

v19
      ekdikounteV (edkikew) part. "take revenge" - revenge, avenge. The word implies a wrong has been done for which a suitable reaction is called for. A believer, standing under the grace of God in Christ, cannot wield the sword of revenge against another sinner, rather we should leave the matter in God's hands, for his mercy, or his wrath. The wrath is best witnessed at Gethsemane. "We give place to wrath only when we wait patiently for the proper time for our deliverance, praying in the meantime that those who now trouble us may repent and become our friends", Calvin.
      dote topon "leave room" - give place. "Let the wrath of God have its way", Moffatt.
      th/ orgh/ (h) "God's wrath" - the wrath. "God" is understood.

v20
      Proverbs 25:21-22, LXX. Render help to anyone in need. The enemy is not necessarily someone outside the fellowship.
      anqrakaV puroV "burning coals" - coals of fire. An image of "the burning pangs of shame and contrition", Cranfield.
      swreuseiV (swreuw) fut. "heap" - you will pile up. The piling up of good deeds toward an enemy serves to stir their bitter conscience and hopefully move them toward reconciliation with God.