Sin.

Sin never slew a soul unless there went
Along with it some tempting blandishment.

Sin no existence; nature none it hath,
Or good at all, as learned Aquinas saith.

Sin leads the way, but as it goes, it feels
The following plague still treading on his heels.

When once the sin has fully acted been,
Then is the horror of the trespass seen.

Sinners confounded are a twofold way,
Either as when, the learned schoolmen say,
Men's sins destroyed are when they repent,
Or when, for sins, men suffer punishment.

There's no constraint to do amiss,
Whereas but one enforcement is.