unfailing: something that keeps going or holds steady without giving out, the way a stream that runs all year does
The picture behind this word is water. In Israel most streambeds carry water only after the winter rains and lie as dry gravel the rest of the year. A few keep running through the hot months, and that is what this word first names: the streambed you can count on. Amos 5:24 is the famous case, where justice is to roll on like the one stream that never quits.
From water the word stretches to anything that does not give out, which is why it is not really a word about power. Something can be חָזָק, strong in the sense of forceful, in a single moment. This word asks a different question: does it hold? What it describes falls into three kinds:
- a streambed, river, or sea that keeps to its steady flow
- a nation, a settlement, or the footings of the earth that have been there a long time and are still there
- a bow, a rock ledge, or an ache that does not give way or let up
English has to reach for a different word almost every time, and older translations often settled on "strong" or "mighty". That is not so much wrong as thin. When justice is asked to come like a stream that never fails, the force of the line is that it keeps coming, not that it comes hard.
The word left its mark on the Hebrew calendar too: the autumn month was called אֵיתָנִים, the month of the streams that are still running when everything else has dried up.
Nuances
Whether the Hebrew text of Proverbs 13:15 is sound, and so whether this word stands in the verse at all. The received Hebrew ends the line with אֵיתָן, giving "the way of the treacherous is hard", while the Septuagint and the Peshitta reflect a graphically similar אֵידָם, "their ruin", which yields a tidier antithesis with the first half of the proverb.
- contestedThe received Hebrew stands, and אֵיתָן here carries a hard or unyielding sense, an extension of its normal range.; BDB, s.v. אֵיתָן; HALOT, s.v. אֵיתָן
- contestedאֵיתָן is a copying error for אֵידָם, "their ruin", the reading behind the Septuagint and the Peshitta.; William McKane, Proverbs: A New Approach (Old Testament Library); Michael V. Fox, Proverbs 10-31 (Anchor Yale Bible)