While there is nothing wrong with having material possessions, extravagance that comes at someone else’s expense is sin. Indeed, extravagance is no better than burglary when it exists in the face of need, for we commit robbery not only in what we take from others but also in what we keep for ourselves. The Bible condemns extravagant lifestyles, especially the book of Amos, which contrasts the complacency and opulence of the rich with the misfortune of the poor and oppressed:
Woe to you who are complacent in Zion, and to you who feel secure on Mount Samaria, you notable men of the foremost nation, to whom the people of Israel come! … You lie on beds inlaid with ivory and lounge on your couches. You dine on choice lambs and fattened calves. … You drink wine by the bowlful and use the finest lotions, but you do not grieve over the ruin of Joseph (Amos 6:1, 4, 6).
As J.A. Motyer points out in his commentary, The Day of the Lion, “It was a shrewd thrust for Amos to describe the nation as Joseph – the lad who wailed his heart out in a deep pit while his brothers sat down to eat (Genesis 37:23-25; 42:21).” Rather than mourning with those who mourn and weeping with those who weep (Romans 12:15), the affluent Israelites of Amos’ day engaged in brazen acts of extravagance which deprived the poor of their basic needs. Amos was intent on jarring his audience into an awareness of how their extravagant lifestyles affected the welfare of those around them.
(Taken from Extravagance at the Generous Giving website)