Albert Barnes Commentary Hosea 5:13

"When Ephraim saw his sickness, and Judah [saw] his wound, then went Ephraim to Assyria, and sent to king Jareb: but he is not able to heal you, neither will he cure you of your wound." — Hosea 5:13 (ASV)

When Ephraim saw his sickness - Literally, “And Ephraim saw,” that is, perceived it. God proceeds to tell them how they acted when they felt those lighter afflictions, the decline and wasting of their power. The “sickness” may further mean the gradual inward decay; the “wound,” blows received from without.

And sent to king Jareb - Or, as in the English margin, “a king who should plead, or, an avenging king.” The “hostile king” is probably the same Assyrian Monarch whom both Israel and Judah courted, who was the destruction of Israel and who weakened Judah.

Ahaz king of Judah did send to Tiglath-Pileser king of Assyria to come and save him, when the Lord brought Judah low; and Tiglath-Pileser king of Assyria came unto him and distressed him, but strengthened him not (2 Chronicles 28:19–20). He who held his throne from God sent to a pagan king, I am thy servant and thy son; come up and save me out of the hand of the king of Syria, and out of the hand of the king of Israel, which rise up against me (2 Kings 16:7–8). He emptied his own treasures and pillaged the house of God in order to buy the help of the Assyrian, and he taught him an evil lesson against himself concerning his wealth and his weakness.

God had said that, if they were faithful, five shall chase an hundred, and an hundred put ten thousand to flight (Leviticus 26:8). He had pronounced him cursed, who trusted in man, and made flesh his arm, and whose heart departed from the Lord (Jeremiah 17:5). But Judah sought man’s help, not only apart from God, but against God. God was bringing them down, and they, by man’s aid, would lift themselves up. “The king” became an “avenger,” for, “whoever, when God is angry, strives to gain man as his helper, finds him God’s avenger, who leads into captivity God’s deserters, as though he were sworn to avenge God.”