[The Christian life] is not a life which at first is fairly broad, and which as you go on becomes narrower and narrower. No! The gate itself, the very way of entering into this life, is a narrow one. … Too often the impression is given that to be a Christian is after all very little different from being a non-Christian, that you must not think of Christianity as a narrow life, but as something most attractive and wonderful and exciting, and that you come in in crowds. It is not so according to our Lord. The gospel of Jesus Christ is too honest to invite anybody in that way. It does not try to persuade us that it is something very easy, and that it is only later on that we shall begin to discover it is hard. The gospel of Jesus Christ openly and uncompromisingly announces itself as being something which starts with a narrow entrance, a strait gate. …
We are told at the very outset of this way of life, before we start on it, that if we would walk along it there are certain things which must be left outside, behind us. There is no room for them, because we
have to start by passing through a strait and narrow gate. I like to think of it as a turnstile. It is just like a turnstile that admits one person at a time and no more. And it is so narrow that there are certain things which you simply cannot take through with you. It is exclusive from the very beginning, and it is important that we should look at this sermon in order to see some of the things which must be left behind.
The first thing we leave behind is what is called worldliness. We leave behind the crowd, the way of the world. … The Christian way of life is not popular. … You cannot take the crowd with you into the Christian life; it inevitably involves a break.
Studies in the Sermon on the Mount, ii, pp. 220-1