Matthew 5:8

From Martin Lloyd-Jones (Studies in the Sermon on the Mount):

"What is meant by this term, 'the heart'? According to the general scriptural usage of the term, the heart means the centre of the personality. It does not merely mean the seat of the affections and the emotions. This Beatitude is not a statement to the effect that the Christian faith is something primarily emotional, not intellectual or pertaining to the will. Not at all. The heart in Scripture includes the three. It is the centre of man's being and personality; it is the fount out of which everything else comes. It includes the mind; it includes the will; it includes the heart. It is the total man; and that is the thing which our Lord emphasizes. 'Blessed are the pure in heart'; blessed are those who are pure, not merely on the surface but in the centre of their being and at the source of their every activity. It is as deep as that. Now that is the first thing; the gospel always emphasizes that. It starts with the heart."