Speaking in 1948 Lloyd-Jones is commenting on 1 John 1:3 (“And truly our fellowship is with the Father, and with his Son Jesus Christ.”):
Let me put it negatively like this: Christians are not simply people who are primarily concerned about the application of Christian principles and Christian teaching in all their relationships and departments of life. They are concerned about that, but that is not the thing that truly makes them Christian. How easy it is today to think of Christianity like that, and how many people do so.
Take a popular classification of a Christian and a non-Christian. Christian people are those who are concerned with the ethics and the teaching of the New Testament and who see the desperate need of applying them to the world today. Now I grant that that is part of the Christian life, but if our conception of it stops at that, we have not, in a sense, got anywhere near the definition given by the Apostle [John] here. No, the Christian life is not essentially an application of teaching; it is a fellowship, a communion with God Himself and nothing less.
Or let me even put it like this: To be a Christian does not merely mean that you hold orthodox opinions on Christian teaching. I put it like that because I think that this is another important emphasis. Perhaps to some of us, and particularly perhaps to those of us who are more evangelical than others, this is the greatest danger of all. We recognise at once that there are certain people who call themselves Christian who hold views that are the antithesis of the Christian faith. There are people calling themselves Christians who deny the unique deity of Christ; to us they cannot be Christian. There are certain things, we say, which are absolutely essential and there can be no parleying or discussion about them. They are essential to the faith, there is an irreducible minimum, but there are people calling themselves Christian who deny some of these things, indeed perhaps all of them together. They may even hold office in the Christian Church and yet be uncertain about the person of the Lord, denying His miracles, denying the fact of His resurrection, denying the atoning value of His death.
Now to us that is quite clear. We see that someone like that, whatever he may call himself, cannot, according to the New Testament, be a Christian; there are certain things which Christians must believe; there are certain tenets to which they must subscribe; there are certain definitions which they must make their own and about which they say, ‘I am certain.’ We see that orthodoxy is essential, but my point here, and I am anxious to impress and stress this, is that to hold the right views, to subscribe to the right doctrine, even to be defenders of the right doctrine, does not of necessity make people Christians. No, while the Christian must hold right views and doctrines, that is not the essence of the Christian life and Christian position.
Let me even put it like this: To believe that your sins are forgiven by the death of Christ is not enough. Even to be sound on the whole doctrine of justification by faith only–the great watchword of the Protestant Reformation–that is not enough. That can be held as an intellectual opinion, and if people merely hold on to a number of orthodox opinions, they are not, I repeat, in the truly Christian position. The essence of the Christian position and of the Christian life is that we should be able to say, ‘Truly my fellowship is with the Father, and with His Son Jesus Christ.’
…This, let me emphasise again, is the essence, the summum bonum, of the Christian life; it is the theme, the objective of everything that has been done by the Lord Jesus Christ, who did not come to earth merely to give us an exalted teaching which we can apply to human relationships, though that is there and it follows; He did not come merely to save us from hell; He came to bring us into fellowship with the Father and with Himself.
Martyn Lloyd-Jones, Fellowship with God, p. 72-73