The two images—a rotten tooth and a sprained foot—clearly show how dangerous it is to trust an unreliable person. This will surely result in failure, which will only make things worse in a crisis situation.
In Ezekiel 29:1–21, the Lord punishes Egypt because in this way, they deceived the people of Israel.
In Proverbs 25:7 we read, When they grasped you with the hand, you broke and tore all their shoulders; and when they leaned on you, you broke and made all their loins to shake.
So, we find the same imagery here as in Proverbs 25:19. This also shows how seriously the Lord regards worthless help. And at the same time, this is an encouragement to call upon the Lord first of all when in need and expect help from him (see Psalm 146:1–10: Put not your trust in princes
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19 Trusting in a treacherous man in time of trouble is like a bad tooth or a foot that slips.