To understand better this passage of Amos can be useful connect it with the chapter 5 of Isaiah, to grasp the general meaning of the divine message to the Israelites (especially northern ones). These two prophets painted – even if between them did pass about seventy years - Amos preceding Isaiah – an inside view of the spiritual situation of Israel. Their descriptions are striking similar. In general, the components of God’s people in that epoch – and, the leading men of Israel, particularly - overjoyed on their wealths, neglecting their spiritual need, and that of their subordinates, also.
For example, the wealthy שׁאננים (Amo 6:1), that is, ‘those who are at ease’, or, as Isaiah (5:13) said, the מתי כבודו, that is ‘the glorious (or, ‘honourable’) men’, lived a life of ease (Amo 6: 4, 5; Isa 5:8, 9), sprawling themselves on the sofas (Amo 6:4), annexing to their estates houses upon houses, and fields upon fields (Isa 5:8a), wine boozing themselves, from the morning to the evening (Isa 5:11, 22), even drinking from the מזרקי (Amo 6:6), literally, ‘jams shedding wine’. There, it was no lack of music (Amo 6:5; Isa 5:12). Plainly, according their lifestyle, they weren’t interested about the spiritual degradation in which Israel lived (Amo 6:6; Isa 5:12). They changed the justice into wickedness (Amo 6:12; Isa 5:7, 20), being corrupted and neglecting to make justice on favour of the defrauded ones (Isa 5:23).
Well, if we take account of this background, the verse 13 – we are disserting – seems to be structured into a synthetic parallelism’s frame. In this kind of parallelism, the second part of the verse amplifies and clarifies the concept expressed in the first part of it.
This was hinted yet by Keil&Delitzsch, inside their Commentary on the OT: “These great men, however, rejoice thereby in לֹא דָבָר, ‘a nothing’, or a thing which has no existence. What the prophet refers to may be seen from the parallel clause, viz., their imaginary strength (chōzeq). They rested this hope upon the might with which Jeroboam had smitten the Syrians, and restored the ancient boundaries of the kingdom. From this might they would take to themselves (lâqach, to take, not now for the first time to create, or ask of God) the horns, to thrust down all their foes. ‘Horns’ are signs and symbols of power (cf. Deu 33:17; 1Ki 22:11); here they stand for the military resources, with which they fancied that they could conquer every foe.”
Those wealthy and arrogant men – through the wine effect acting as catalyst – fooled themselves, rejoicing over the “void”, or, “nothing”, that is on their power (‘horns’) they imagined to possess (Amo 6:13; Isa 5:15, 19, 21).
Very interestingly, we may note that the link between ‘wine’, ‘illusion’ (= “nothing, void” [דבר לא]) of power, and ‘horns’ [קרנים] was utilized also by extraBible writers. For example, Ovid (some centuries after Amos) in his Ars Amatoria (Book I, Part VII) wrote: “Vina parant animos faciuntque caloribus aptos / cura fugit multo diluiturque mero. / Tunc veniunt risus, tum pauper corna sumit […].” (“Wine rouses courage and is fit for passion / care flies, and deep drinking dilutes it. / Then laughter comes, the poor man dons the horns […].”).
What Amos said in 6:13… in other words.