Walk through Amos, verse by verse, with the great Bible Commentaries of Matthew Henry (1662 - 1714) & Adam Clarke (1760 - 1832)
6:13
Ye which rejoice in a thing of nought, which say, Have we not taken to us horns by our own strength? KJV
{And ye be glad in nought, and ye say, Whether not in our strength we took to us horns?}
Wycliffe's Bible
Ye which rejoice in a thing of naught - In your idols: for an idol is nothing in the world.