Jesus gave His disciples a new commandment just before He went to the cross. They were to love one another as He had loved them (Jn. 13:34). It is this last phrase that makes Jesus' command impossible to fulfill without God's grace.
What is the distinctive feature of the love of Christ? Surely, it is the cross on which He died for us. So when He tells me to love my brother as He loved me, it is a call to follow His example and to die to self in my relationship with my brother. Self-denial is to characterize my relationship with other members in Christ's Body. This and nothing less than this is true Christian love. When we are told that "we ought to lay down our lives for the brethren" (1 Jn. 3:16), it is not a reference to physical death, but to something far more difficult. It is easier to die once as a martyr than to lay down our self-life many times every day in our relationship with our fellow-believers. But it is to the latter that Jesus calls us.
Such sacrificial, unselfish love is the fundamental law of the body of Christ. One who does not carry the cross and choose the way of self-denial cannot fulfil his function in Christ's Body.
Why are we offended and irritated with other Christians? Surely, because Self is still on the throne of our lives. We consider ourselves so important, that we feel we must be respected and consulted by others. We feel that others must behave and order their affairs as we want them to. We expect others to be kind and considerate to us, to 'make much' of us and praise us. Such feelings and expectations are clear evidence of the fact that we know nothing of the cross experientially. Our lives are still dominated by selfishness and revolve exclusively around Self and it's interests.
True Christian fellowship can never be experienced among believers, if the love of the cross is not made the fundamental rule in the conduct of their relationships. Apart from such love, whatever goes by the name "fellowship" will only be social friendship and not the true communion of the Body of Christ. Such social friendship exists in worldly clubs too. Sadly, many Christian churches and groups are no better than clubs!
The members of a Christian fellowship should be closely interlocked, one with the other. God has not called us to be an assortment of dismembered limbs thrown together as in an anatomy laboratory, but to be united one with the other as parts of a living organism like the human body. But there is a price to be paid if this is to become a reality - the price of each member denying himself for the sake of others. Blessed indeed is that Christian group where all the members are willing to live by this rule.