Whoever loves his brother lives in the light, and there is nothing in him to make him stumble. 1 John 2:10, N.I.V. RC 222.1
They [the disciples] rejoiced in the sweetness of communion with saints.... But gradually a change came. The believers began to look for defects in others. Dwelling upon mistakes, giving place to unkind criticism, they lost sight of the Saviour and His love. They became more strict in regard to outward ceremonies, more particular about the theory than the practice of the faith. In their zeal to condemn others, they overlooked their own errors. They lost the brotherly love that Christ had enjoined, and, saddest of all, they were unconscious of their loss. They did not realize that happiness and joy were going out of their lives and that, having shut the love of God out of their hearts, they would soon walk in darkness. RC 222.2
John, realizing that brotherly love was waning in the church, urged upon believers the constant need of this love. His letters to the church are full of this thought. “Beloved, let us love one another,” he writes; “for love is of God; and every one that loveth is born of God, and knoweth God.” ... RC 222.3
It is not the opposition of the world that most endangers the church of Christ. It is the evil cherished in the hearts of believers that works their most grievous disaster and most surely retards the progress of God's cause. There is no surer way of weakening spirituality than by cherishing envy, suspicion, faultfinding, and evil surmising. On the other hand, the strongest witness that God has sent His Son into the world is the existence of harmony and union among men of varied dispositions who form His church. This witness it is the privilege of the followers of Christ to bear. But in order to do this, they must place themselves under Christ's command. Their characters must be conformed to His character and their wills to His will. RC 222.4
“A new commandment I give unto you,” Christ said, “That ye love one another; as I have loved you, that ye also love one another” (John 13:34). What a wonderful statement; but, oh, how poorly practiced! In the church of God today brotherly love is sadly lacking. Many who profess to love the Saviour do not love one another. Unbelievers are watching to see if the faith of professed Christians is exerting a sanctifying influence upon their lives; and they are quick to discern the defects in characters, the inconsistencies in action. RC 222.5
Let Christians not make it possible for the enemy to point to them and say, Behold how these people, standing under the banner of Christ, hate one another. Christians are all members of one family, all children of the same heavenly Father, with the same blessed hope of immortality. Very close and tender should be the tie that binds them together.—The Acts of the Apostles, 547-550. RC 222.6