8 To sum up, all of you be harmonious, sympathetic, brotherly, kindhearted, and humble in spirit; 9 not returning evil for evil or insult for insult, but giving a blessing instead; for you were called for the very purpose that you might inherit a blessing. 1 Peter 3:8-9 (NASB)
We are commanded to have unity among the brethren, but that unity must be based on our union with Christ. Jesus prayed that His church would have unity through Him in John 17, but how does the Bible describe it? Here are a few passages. The first two describe union with Him as Christ being in us.
14 For this reason I bow my knees before the Father, 15 from whom every family in heaven and on earth derives its name, 16 that He would grant you, according to the riches of His glory, to be strengthened with power through His Spirit in the inner man, 17 so that Christ may dwell in your hearts through faith; and that you, being rooted and grounded in love, 18 may be able to comprehend with all the saints what is the breadth and length and height and depth, 19 and to know the love of Christ which surpasses knowledge, that you may be filled up to all the fullness of God. Ephesians 3:14-19 (NASB)