This is a fairly common prophetic phrase. Figuratively speaking, the Lord has an arm of justice and an arm of mercy. When the scriptures say that ’his hand is stretched out still,’ it can mean that the Lord plans to be even more merciful or punitive, depending on which arm is stretched out. In this instance, it means that the Lord‘s hand of justice is ’stretched out still’—that He has more punishments planned for the wicked in Israel. These other punishments are described in later verses and in chapter 20.