What are the eternal consequences of sin?

The eternal consequence of sin must of necessity obtain with those against whom we sin. 

If a man refuses to pay a just debt, he not only chooses to do wrong, but weakens his moral force, and lays himself open to temptation. 

The violations of the Law of Love is a fearful retribution, and we are obliged to trace the consequences of such acts and realise the mischief, which results, for all outward surroundings are the outgrowth of the internal state. 

As the spirit author in Letters from a Spirit [unknown] avouches—Oh—if humanity could only see how mean and poor all that earth can give is in exchange for integrity, purity and holiness, the prodigals would cease from their swine's husks, and go to the Father's house, and eat angel's food, and grow worthy of the high calling of His sons. Evil can never be good either to the doer or the sufferer therefrom, and only the Divine Providence could overrule it to any worthy ending.

Praise and glory His Holy name, Who permits the worst of our evils from affecting those whom we injure.