In the introduction to Martyn Lloyd-Jones‘ Studies in the Sermon on the Mount, he writes this:

I suggest to you that [the Sermon on the Mount] is the best means of evangelism. Surely we all ought to be urgently concerned about this at the present time. The world today is looking for, and desperately needs, true Christians. I am never tired of saying that what the Church needs to do is not to organize evangelistic campaigns to attract outside people, but to begin herself to live the Christian life. If she did that, men and women would be crowding into our buildings. They would say, ‘What is the secret of this?’

He goes on to compare Christianity with communism (a serious threat in the 1950’s) and how Christianity, when lived out, provides in reality what communism promises but fails to provide.

While communism may not be the largest challenge to the church today, the need for living out the Christian life is still more urgent. We have the answer to what ails society but our failure to display it in our lives prevents the answer from being accepted.

Mr. Lloyd-Jones calls us to face up to our failures in this regard, repent and begin really living the life of faith.