The paths of their way are turned aside - Noyes renders this, "The caravans turn aside to them on their way." Good, "The outlets of their channel wind about." Rosenmuller, "The bands of travelers direct their journey to them." Jerome, "Involved are the paths of their steps." According to the interpretation of Rosenmuller, Noyes, Umbreit, and others, it means that the caravans on their journey turn aside from their regular way in order to find water there; and that in doing it they go up into a desert and perish. According to the other interpretation, it means that the channels of the stream wind along until they diminish and come to nothing. This latter I take to be the true sense of the passage, as it is undoubtedly the most poetical. It is a representation of the stream winding along in its channels, or making new channels as it flows from the mountain, until it diminishes by evaporation, and finally comes to nothing.
They go to nothing - Noyes renders this very singularly, "into the desert," - meaning that the caravans, when they suppose they are going to a place of refreshment, actually go to a desert, and thus perish. The word used here, however תהוּ tôhû, does not occur in the sense of a desert elsewhere in the Scriptures. It denotes nothingness, emptiness, vanity (see Genesis 1:2), and very appropriately expresses the nothingness into which a stream vanishes when it is dried up or lost in the sand. The sense is, that those streams wander along until they become smaller and smaller, and then wholly disappear. They deceive the traveler who hoped to find refreshment there. Streams depending on snows and storms, and having no permanent fountains, cannot be confided in. Pretended friends are like them. In times of prosperity they are full of professions, and their aid is proffered to us. But we go to them when we need their assistance, when we are like the weary and thirsty traveler, and they disappear like deceitful streams in the sands of the desert.

The paths of their way - They sometimes forsake their ancient channels, which is a frequent case with the river Ganges; and growing smaller and smaller from being divided into numerous streams, they go to nothing and perish - are at last utterly lost in the sands.

The paths of their way are turned aside,.... That is, the waters, when melted by the heat of the sun, and the warmth of the weather, run, some one way, and some another in little streams and windings, till they are quite lost and the tracks of them are no more to be seen; denoting that all appearance of friendship was quite gone, and no traces of it to be found:
they go to nothing, and perish: some of them are lost in little meanders and windings about, and others are exhaled by the heat of the sun, and go into "Tohu", as the word is, into empty air; so vain and empty, and perishing, were all the comforts he hoped for from his friends; though some understand this of the paths of travellers in the deserts being covered in the sand, and not to be seen and found; of which see Pliny (z).
(z) Nat. Hist. l. 6. c. 29.

turned aside--rather, "caravans" (Hebrew, "travellers") turn aside from their way, by circuitous routes, to obtain water. They had seen the brook in spring full of water: and now in the summer heat, on their weary journey, they turn off their road by a devious route to reach the living waters, which they remembered with such pleasure. But, when "they go," it is "into a desert" [NOYES and UMBREIT]. Not as English Version, "They go to nothing," which would be a tame repetition of the drying up of the waters in Job 6:17; instead of waters, they find an "empty wilderness"; and, not having strength to regain their road, bitterly disappointed, they "perish." The terse brevity is most expressive.

18 The paths of their course are turned about,
They go up in the waste and perish.
19 The travelling bands of Tma looked for them,
The caravans of Saba hoped for them;
20 They were disappointed on account of their trust,
They came thus far, and were red with shame.
As the text is pointed, ארחות, Job 6:18, are the paths of the torrents. Hitz., Ew., and Schlottm., however, correct ארחות, caravans, which Hahn even thinks may be understood without correction, since he translates: the caravans of their way are turned about (which is intended to mean: aside from the way that they are pursuing), march into the desert and perish (i.e., because the streams on which they reckoned are dried up). So, in reality, all modern commentators understand it; but is it likely that the poet would let the caravans perish in Job 6:18, and in Job 6:19. still live? With this explanation, Job 6:19. drag along tautologically, and the feebler figure follows the stronger. Therefore we explain as follows: the mountain streams, נחלים, flow off in shallow serpentine brooks, and the shallow waters completely evaporate by the heat of the sun. בתּהוּ עלה signifies to go up into nothing (comp. Isaiah 40:23), after the analogy of בעשׁן כּלה, to pass away in smoke. Thus e.g., also Mercier: in auras abeunt, in nihilum rediguntur. What next happens is related as a history, Job 6:19., hence the praett. Job compares his friends to the wady swollen by ice and snow water, and even to the travelling bands themselves languishing for water. He thirsts for friendly solace, but the seeming comfort which his friends utter is only as the scattered meandering waters in which the mountain brook leaks out. The sing. בּטח individualizes; it is unnecessary with Olsh. to read בּטחוּ.

Perish - They are gone out of their channel, flowing hither and thither, 'till they are quite consumed.