Behold, the days come, saith the LORD, that the plowman shall overtake the reaper, and the treader of grapes him that soweth seed; and the mountains shall drop sweet wine, and all the hills shall melt.
Behold, the days come - at the future restoration of the Jews to their own land.
That the plowman shall overtake the reaper, and the treader of grapes him that soweth seed - fulfilling Leviticus 26:5, "Your threshing shall reach unto the vintage, and the vintage shall reach unto the sowing time; and ye shall eat your bread to the full, and dwell in your land safely"). Such shall be the abundance, that the harvest and vintage can hardly be gathered before the time for preparing for the next crop shall come. Instead of the greater part of the year being spent in war, the whole shall be spent an sowing and reaping the fruits of the earth. Compare Isaiah 65:21-23 ("They shall build houses, and inhabit them; and they shall plant vineyards, and eat the fruit of them. They shall not build, and another inhabit; they shall not plant, and another eat ... They shall not labour in vain, nor bring forth for trouble: for they are the seed of the blessed of the Lord, and their offspring with them") as to the same period.
Soweth seed - literally, draweth it forth, namely, from the sack, in order to sow it.
And the mountains shall drop sweet wine - margin, 'new wine;' an appropriate image, as the vines in Palestine were trained on terraces at the sides of the hills. Derived from Joel 3:18 ("The mountains shall drop down new wine"), whereby Amos gives inspired sanction to Joel's prophecies.