Matthew 5:27-28

In his heart.

The heart or will is, in man, the seat of virtue or vice.

I. Actions must be our invariable touchstone of truth whilst we sojourn in this state of imperfect knowledge and comparative obscurity, where expression is the only avenue to sentiment, and action the only publisher of intention.

II. Actions are the only public representatives of our private sentiments.

1. So many channels through which the heart discharges its flow of various passions.

2. So many mirrors by the reflection of which the internal dispositions of the soul become externally visible.

III. Actions viewed in a moral light are to the soul what

(1) streams are to the fountain;

(2) branches are to the root.

Branches have no existence but what they derive from the root. Streams have no existence but what they derive from the fountain. Actions have no moral existence but that which they derive from the heart.
When God judges man, the heart is the rule of judgment.

1. The heart, the source of these actions, is to Him uncovered

2. The heart, having the principle of religion so strong as to prevent an unlawful enjoyment, will likewise be sufficiently strong to prevent an unlawful resolution.

3. The depraved heart is before God of the same criminality as the depraved life, and exposes us to the same punishment from God. Let us therefore eternally renounce every inclination inconsistent with religion and reproachful to humanity. Let us cultivate purity of heart. (David Lamont, D. D.)