1 Thessalonians 4:9-12 (NKJV) But concerning brotherly love you have no need that I should write to you, for you yourselves are taught by God to love one another; 10 and indeed you do so toward all the brethren who are in all Macedonia. But we urge you, brethren, that you increase more and more; 11 that you also aspire to lead a quiet life, to mind your own business, and to work with your own hands, as we commanded you, 12 that you may walk properly toward those who are outside, and that you may lack nothing.
V9 “But concerning brotherly love you have no need that I should write to you, for you yourselves are taught by God to love one another…” Brotherly love = the love in relationships as organizations, etc. Here, the organization is the spiritual brothers. The Greek word is (G5360) φιλαδελφία philadelphia, which means brotherly love. “In profane Greek (one papyrus example) and lxx the word means love of those actually kin by blood, but in the N.T. it is the kinship in the love of Christ as here” (Robertson’s Word Pictures). God teaches us this love. We need to remember and practice it. Compare Psalm 133:1, Proverbs 6:16-19, 1 Peter 1:22, and 1 John 3:14. Love is a choice; it is a decision with emotion or not. The actions of love are found in 1 Corinthians 13:4-8. Note, God is a teacher. This is teaching, not decreeing as a nano-manager would. “Taught by God” is the Greek word (G2312) θεοδίδακτος theodídaktos, which means God taught. It is used one time. Compare John 6:45.
V10 “…and indeed you do so toward all the brethren who are in all Macedonia. But we urge you, brethren, that you increase more and more…” The Thessalonians do believe this and practice it. We need each other for encouragement, fellowship, mutual help, prayer, correction, reminders, counsel, and many other things. The brethren (brothers and sisters) are the body of Christ. Because of this, God has given various gifts for service. These gifts are needed to carry out the gift and ministry God gives to each believer. Compare Romans 12:4-8, 1 Corinthians 12:12-27, and Ephesians 4:12. Practicing brotherly love must grow. The flesh nature needs to be tamed and learn how to get alone with others, especially the brethren. Many other character traits are rooted in love–kindness, compassion, forgiveness, mercy, helpfulness, etc. We are not to be content with the love and actions we show. We must still grow to love more as in less anger, less wanting to seek revenge, longsuffering, etc. Compare 2 Peter 1:7-8.
V11 “…that you also aspire to lead a quiet life, to mind your own business, and to work with your own hands, as we commanded you…” A quiet life has the idea of being nonargumentive, not being a busy body, not causing trouble or stress in others, helping others, etc. Paul had to remind the Thessalonians to keep working. Imminence regarding the Rapture might have caused some to stop working and just wait for Jesus. This is wrong, because no one knows that day or hour (Matthew 25:13). The Apostles having authority gave a command to work. Jesus worked until He began His ministry, which then was His work. Some benefits of working is satisfaction, meeting our needs and hopefully helping others if needed, good physically to be moving, fulfilling God’s purpose for us to work, opportunity to be a witness, etc. When we work we must be diligent whether the boss is observing or not. The work we must do must be first class as much as is possible. We are a witness for Jesus. In God’s eyes, any God honoring work is good whether janitor or CEO.
V12 “…that you may walk properly toward those who are outside, and that you may lack nothing.” Walk means daily life which implies a Christian worldview, lifestyle, and rules. Those “outside” are non-believers. Living a god honoring Christian life is a witness to how great society would be if everyone lived as a Biblical Christian. The Greek word “properly” (also translated honestly) is (G2156)εὐσχημόνως euschēmónōs, which means decently and honorably (Romans 13:13 and 1 Corinthians 14:40). Our daily life in public and private is to be godly and in good order, not being lazy, doing good work, and showing godly character traits.