Here are some quotes from Life Together by Drietrich Bonhoeffer:-

“He who looks upon his brother should know that he will be eternally united with him in Jesus Christ.”

“I am a brother to another person through what Jesus Christ did for me and to me; the other person has become a brother to me through what Jesus Christ did for him.”

“What determines our brotherhood is what that man is by reason of Christ. Our community with one another consists solely in what Christ has done to both of us.”

“Christian brotherhood is not an ideal which we must realise; it is rather a reality created by God in Christ in which we may participate.”