Ephraim. The mention of Ephraim is not "perplexing". See explanation in next verse, and in the events of Judges 12:1-6. Jdg 12:17, Jdg 12:18: viz. the introduction of idolatry. It is sin which is spoken of. See Psalms 78:57, "deceitful bow". Compare Hosea 7:16; Hosea 10:6-8.
carrying bows: i.e. though equipped as bowmen, yet were faithless. This is transferred to the moral application.