God proclaims judgement not only on the capital of Syria (Damascus) but also Israel's 10 northern tribes known as Ephraim. Damascus is one of the great cities of the ancient world, and the capital of the ancient nation of Syria. Syria is positioned to the immediate north-east of Israel, and the northern tribes, around the Sea of Galilee, had constant contact and interaction with Syria.
With the coming Assyrian judgment, Damascus would be reduced to a heap of ruins.
As is often the case, the northern kingdom of Israel is referred to by its dominate tribe, Ephraim. God's people had fallen so far into idoloatry that they were now being judged along with a heathen nation who did not honor God. At this time, Israel and Syria were closely aligned against Judah. Since they are such close friends, God will announce His judgment against Ephraim, against Israel, at the same time He speaks to Syria! 2 Kings 15:29 and 16:9 describe the fulfillment of this prophecy.
If we think God's judgment is harsh, we do not understand the evilness involved in idolatry which often involved prostitution and child sacrifice as part of worship.
God is long-suffering and merciful and longs to bring us back into relationship with Him.
In their disobedience, Ephraim had turned to idols and are now realizing that these idols had no power. God's judgment is a reminder to retrun to worshipping Him alone.
David Guzik said this about this chapter. "Israel was not at the mercy of circumstances or their enemies; they were at the mercy of God." We too are always at the mercy of God, instead of our circumstances and enemies.
See also - Lessons: The Names of God