Commentators unanimously explain that if God's own covenant people, Judah, must drink the 'cup' of His wrathful discipline, then Edom, a nation hostile to God, cannot possibly escape. This 'greater-to-lesser' argument highlights the certainty of divine justice. As the Apostle Peter later wrote, if judgment begins with the family of God, the outcome for those who disobey will be even more severe (1 Peter 4:17).