The children of Ephraim - The sons of Ephraim; that is, the descendants of Ephraim; the tribe of Ephraim. Ephraim was one of the “largest” of the tribes of Israel, and was the “chief” tribe in the rebellion, and hence, the term is often used to denote the “ten” tribes, or the kingdom of Israel, in contradistinction from that of Judah. See Isaiah 7:2, Isaiah 7:5,Isaiah 7:8-9, Isaiah 7:17; Isaiah 11:13; Isaiah 28:1. The word is evidently used in this sense here, not as denoting that one tribe only, but that tribe as the head of the revolted kingdom; or, in other words, the name is used as representing the kingdom of that name after the revolt. See 1 Kings 12. This verse evidently contains the gist or the main idea of the psalm - to wit, that Ephraim, or the ten tribes, had turned away from the worship of the true God, and that, in consequence of that apostasy, the government had been transferred to another tribe - the tribe of Judah. See Psalms 78:67-68.
Being armed - The idea in this phrase is, that they had abundant means for maintaining their independence in connection with the other tribes, or as a part of the nation, but that they refused to cooperate with their brethren.
And carrying bows - Margin, “throwing forth.” Literally, “lifting up.” The idea is, that they were armed with bows; or, that they were fully armed.
Turned back in the day of battle - That is, they did not stand by their brethren, or assist them in defending their country. There is probably no reference here to any particular battle, but the idea is, that in the wars of the nation - in those wars which were waged for national purposes - they refused to join with the tribes of Judah and Benjamin in defense of the lawful government.