﴿ ذَٰلِكَ بِأَنَّهُمْ كَانَت تَّأْتِيهِمْ رُسُلُهُم بِٱلْبَيِّنَٰتِ فَكَفَرُوا۟ فَأَخَذَهُمُ ٱللَّهُ ۚ إِنَّهُۥ قَوِىٌّۭ شَدِيدُ ٱلْعِقَابِ ﴾

“this, because their apostles had come to them with all evidence of the truth, and yet they rejected it: and so God took them to task - for, verily, He is powerful, severe in retribution!”

In verse 19, it was said: يَعْلَمُ خَائِنَةَ الْأَعْيُنِ (He knows the treachery of the eyes), in other words, eyes that betray the trust. It means the action of a person who would, secretly and surreptitiously, cast a glance over something haram and impermissible for him or her, for example, casts a glance at a non-mahram person with sexual desire, and takes it away in the event someone was around, or casts a glance in a manner that is not noticed by others. All these things are open before Allah Ta’ ala.