John Calvin Commentary Psalms 78:9

"The children of Ephraim, being armed and carrying bows, Turned back in the day of battle." — Psalms 78:9 (ASV)

The children of Ephraim being armed, and shooting with the bow. The sacred writer presents us with an example of this unfaithfulness in the children of Ephraim. As those who are stubbornly set on doing evil are not easily led to repentance and reformation by simple instruction, the punishments with which God afflicted the children of Ephraim are brought forward, and by these it is proved that they were rejected by God. Since they were a warlike people, their turning back in battle was evidence of divine displeasure. And it is expressly declared that they were skillful in shooting with the bow; for it is an additional mark of disgrace to represent those armed with weapons to wound their enemies from a distance as fleeing through fear. This makes it abundantly clear that they had incurred God's displeasure, who not only deprived them of His aid but also made their hearts cowardly in the hour of danger.

The question may be raised here: Why are only the children of Ephraim blamed, when we find a little earlier all the tribes in general included in the same sentence of condemnation? Some commentators refer this to the slaughter of the sons of Ephraim by the men of Gath, who came out against them to recover their cattle which had been plundered from them, 1 Chronicles 7:20, 21, 22.

But this interpretation is too narrow. Perhaps the kingdom of Israel had fallen into decay and had been almost ruined when this psalm was composed. It is therefore better to follow the opinion of other interpreters, who think that by the figure of synecdoche, the children of Ephraim represent the whole people.

But these interpreters overlook the fact—which ought not to be ignored—that the Ephraimites are purposely named because they were instrumental in leading others into the rebellion that took place when Jeroboam set up the calves (1 Kings 12:25–33). We must also remember what has already been said: that towards the end of the psalm, the rejection of the tribe of Ephraim is, not without cause, contrasted with the election of the tribe of Judah.

The children of Ephraim are also mentioned here for comparison, to warn the true children of Abraham by the example of those who cut themselves off from the Church, and yet boasted of the title of the Church without showing holy fruit in their lives. As they surpassed all the other tribes in number and wealth, their influence was too powerful in deceiving the simple; but the prophet now strips them of this, showing that they were deprived of God's help.