What does Isaiah 17:5 mean?
Isaiah is describing the loss of status and wealth that will come upon Israel; the destruction on Damascus will spill over onto them, as well. The prophet has written that Israel will grow from healthy and well-fed to desperately starving (Isaiah 17:3–4). As an illustration, he describes those who are dependent on the gleanings in the Valley of Rephaim to survive.The Valley of Rephaim, southwest of Jerusalem, contained fertile fields of grain. The common practice of the day, as mandated by the old testament law, provided for the poor. During the harvest, the reaper would gather grain in his arms but not pick up the ears of grain that he dropped along the way (Deuteronomy 24:19–21). Those who were destitute could follow behind and gather up the remains of the harvest—the "gleanings"—to live on. The Lord has always had provision in place for those in need.
The glory of Israel had changed so much that instead of being the one who reaps the crops, they had become the one who lives on the gleanings.