Walk through Amos, verse by verse, with the great Bible Commentaries of Matthew Henry (1662 - 1714) & Adam Clarke (1760 - 1832)
4:5
And offer a sacrifice of thanksgiving with leaven, and proclaim and publish the free offerings: for this liketh you, O ye children of Israel, saith the Lord GOD. KJV
{And sacrifice ye praising of bread made sour, and call ye (out about your) willful offerings, and tell ye; for ye, sons of Israel, would so, saith the Lord God.} Wycliffe's Bible
Over a sacrifice of thanksgiving - To the senseless metal, and the unfeeling stock and stone images, from which ye never did, and never could receive any help. Proceed yet farther, and bring free-will offerings; testify superabundant gratitude to your wooden and metallic gods, to whom ye are under such immense imaginary obligations!