Every born again believer knows that he or she is supposed to love the brethren. There is a lot at stake. Jesus told His disciples that Christian unity was the evidence that God loves mankind, and not with just any old love, but with the same love He has for Jesus, His Son (Jn. 17:21-23). Here are just a few of the verses telling believers to love one another:
Rom. 12:10 "Be kindly affectioned one to another with brotherly love; in honour preferring one another."
Rom. 13:8 "Owe no man any thing, but to love one another: for he that loveth another hath fulfilled the law."
Gal. 5:13-14 "For, brethren, ye have been called unto liberty; only [use] not liberty for an occasion to the flesh, but by love serve one another. For all the law is fulfilled in one word, even in this; Thou shalt love thy neighbour as thyself."
1 Thes. 3:12 "And the Lord make you to increase and abound in love one toward another, and toward all men, even as we do toward you."
1 Thes. 4:9 "But as touching brotherly love ye need not that I write unto you: for ye yourselves are taught of God to love one another."
Heb. 10:24 "And let us consider one another to provoke unto love and to good works."
1 Jn. 4:11 "Beloved, if God so loved us, we ought also to love one another."
1 Pet. 4:8 "And above all things have fervent charity among yourselves: for charity shall cover the multitude of sins."
On the other side of the coin, God knows that we will have difficulty loving and obeying Him (Rom. 7:14-25), let alone loving the brethren who are as flawed as we are. That is why He had the Apostle Paul write, "I therefore, the prisoner of the Lord, beseech you that ye walk worthy of the vocation wherewith ye are called, with all lowliness and meekness, with longsuffering, forbearing one another in love; endeavouring to keep the unity of the Spirit in the bond of peace" (Eph. 4:1-3).
Christians, because we are still in the process of becoming like Christ (1 Jn. 3:2), find it difficult, if not impossible, to continually love each other. Paul used the word, "endeavoring" to show that loving one another takes hard work. It requires perseverance. It requires forgiveness. It requires a mirror. For when we look "into the mirror" of God's Word, and we see how flawed we are, it is easier to love those who are a lot like us (Jam. 1:22-25).
God is omniscient, not naive. He knows our spiritual condition, and He knows how two of His children, both being flawed, will inevitably clash. That is why He had Paul write, "If it be possible, as much as lieth in you, live peaceably with all men" (Rom. 12:18). Some Christians might see this as an opportunity for to "write off" those they do not like. However, God has made it clear what He expects of us (Matt. 5:23-24;18:15-17). In other words, do your very best at getting along with your brethren, but regardless of the friction between you, love him.