[af_vet_1981]

Since lust in one’s heart is adultery, everyone has broken their marital vow.

It seems to me this type of statement tends to minimize and normalize the actual physical adultery, that for which the Old Testament Law proscribed the death penalty. Although the New Testament extends the scope of adultery to include lust it does not abrogate the Law.

I understand the New Testament teaching by way of this explanation.

James 1:12-16
Blessed is the man that endureth temptation: for when he is tried, he shall receive the crown of life, which the Lord hath promised to them that love him.
Let no man say when he is tempted, I am tempted of God: for God cannot be tempted with evil, neither tempteth he any
But every man is tempted, when he is drawn away of his own lust, and enticed.
Then when lust hath conceived, it bringeth forth sin: and sin, when it is finished, bringeth forth death.
Do not err, my beloved brethren.

[RoosterRedux]

It seems to me this type of statement tends to minimize and normalize the actual physical adultery

Not at all.

Physical acts are punishable by law and by God. But sins of the mind and heart—though hidden—are judged by God alone, which is far more serious.

Jesus wasn’t minimizing sin; He was exposing its deeper root—our deeper rot. The rot that infects the soul. The infection we humans brought into the world—the source of all its evil.

And if someone asks, “But what about demonic evil?”

Perhaps we invited them in. In fact, we may have caused their fall by our own corruption—“the daughters of men were beautiful” (Genesis 6).

Scripture hints they fell not only from pride, but from desire for what they saw in us. Either way, it was our sin that opened the door—and keeps opening the door into human souls.