49 Here the brothers are all his relatives as well as these intimate friends of Job. In contrast to what a friend should do (show kindness/loyalty), these friends have provided no support whatsoever.
50 The verb בָּגְדוּ (bagédu, “dealt treacherously) has been translated “dealt deceitfully,” but it is a very strong word. It means “to act treacherously [or deceitfully].” The deception is the treachery, because the deception is not innocent—it is in the place of a great need. The imagery will compare it to the brook that may or may not have water. If one finds no water when one expected it and needed it, there is deception and treachery. The softens it considerably: “have not regarded me.”
51 The Hebrew term used here is נָחַל (nakhal); this word differs from words for rivers or streams in that it describes a brook with an intermittent flow of water. A brook where the waters are not flowing is called a deceitful brook (Jer 15:18; Mic 1:14); one where the waters flow is called faithful (Isa 33:16).
52 Heb “and as a stream bed of brooks/torrents.” The word אָפִיק (’afiq) is the river bed or stream bed where the water flows. What is more disconcerting than finding a well-known torrent whose bed is dry when one expects it to be gushing with water (E. Dhorme, Job, 86)?
53 The verb is rather simple—יַעֲבֹרוּ (ya’avoru). But some translate it “pass away” or “flow away,” and others “overflow.” In the rainy season they are deep and flowing, or “overflow” their banks. This is a natural sense to the verb, and since the next verse focuses on this, some follow this interpretation (H. H. Rowley, Job [], 15). But this idea does not parallel the first part of v. 15. So it makes better sense to render it “flow away” and see the reference to the summer dry spells when one wants the water but is disappointed.