If the eye is once inflamed

(Thomas Watson, "The Lord's Prayer")

If we would be kept from actual sins—let us be
careful to avoid all the inlets and occasions of sin.

Do not run into evil company. He who would not
catch the plague—must not go into an infected house.

Guard your senses, which may be the inlets to sin.
Keep the two portals—the eye and the ear. Especially
guard your eyes. Much sin comes in by the eye; the
eye is often an inlet to sin; sin takes fire at the eye.

The first sin in the world, began at the eye. "When
the woman saw that the fruit of the tree was good for
food and pleasing to the eye—she took some and ate
it." Genesis 3:6

Intemperance begins at the eye,
"Do not gaze at wine
when it is red, when it sparkles in the cup. In the end it
bites like a snake and poisons like a viper!" Pr. 23:31-32

Covetousness begins at the eye. "When I saw among
the spoils a goodly Babylonish garment, and a wedge
of gold, I coveted them and took them." Joshua 7:21

The fire of lust begins to kindle at the eye. David walking
upon the roof of his house, saw a woman washing herself,
and she was, says the text, "beautiful to look upon," and
he sent messengers and took her, and defiled himself with
her. 2 Samuel 11:2.
Looking begat lusting!

Therefore watch your eyes! Job made a covenant with
his eyes. Job 31:1. If the eye is once inflamed, it will
be hard to stand out long against sin. If the outworks
are captured by the enemy, there is great danger of the
whole castle being captured!