"Enter by the narrow gate. For the gate is wide and the way is easy that leads to destruction, and those who enter by it are many. For the gate is narrow and the way is hard that leads to life, and those who find it are few." (Matthew 7:13-14 ESV)
"That is the characteristic of this age. We have a tabloid mentality. We want to know a little bit of information about everything. But that is the exact opposite of what we have here. Take this book the Bible, the great old book of sixty-six books, written at different times by different people in different circumstances. In this book there is a great variety of subjects. There is much about creation and history; there is much about births and marriages and deaths and wars. And yet this book is not an encyclopedia. It is a very specialized book. It is the manual of the soul. This book has only one theme from beginning to end, and that one theme is God and man, or man in his relationship to the eternal God. It is not a book that tells you a little about many things. It is a book that tells you everything about that one central theme, and it keeps itself to that. It is a specialist book. And what is true of the book is true of the Master of the book. If ever there was a specialist in this world, it was the Lord Jesus Christ. Look at the things he might have done. Look at the ability, the knowledge, at his command. Yet he deliberately keeps himself to one theme. Had you ever noticed that as you read the four Gospels? There is a sense in which it is true to say that the Lord Jesus Christ had only one sermon, and he went on preaching that one sermon for three years. He varied his illustrations, but there was only one point. And that one essential sermon was about this whole question of the human soul in its relationship to the everlasting God."
~ Martyn Lloyd-Jones, Setting Our Affections upon Glory: Nine Sermons on the Gospel and the Church.
The complete text of this sermon has also been republished in the Christ-centered Preaching of Martyn Lloyd-Jones (Crossway, 2014), and this particular sermon is available online here and free in this PDF.
Etching above is "The Wicket Gate", by Robin Tanner.