78. How do unfaithful husbands and wives treat this holy institution?

They despise it, and thus bring down upon themselves the judgment of God.

Heb. 13:4. Whoremongers and adulterers God will judge.

79. Repeat some passages from Scripture in which impurity is forbidden?

Be not deceived: neither fornicators, nor adulterers, nor effeminate, nor abusers of themselves with mankind, shall inherit the kingdom of God. 1 Cor. 6:9, 10.

Jesus says: I say unto you, that whosoever looketh on a woman to lust after her hath committed adultery with her already in his heart. Matt. 5:28.

Let no corrupt communication proceed out of your mouth! Eph. 4:29.

80. Why is this sin so fearful?

Because it affects both soul and body more than any other sin.