Albert Barnes Commentary Hosea 6:10

"In the house of Israel I have seen a horrible thing: there whoredom is [found] in Ephraim, Israel is defiled." — Hosea 6:10 (ASV)

I have seen a horrible thing - Literally, “what would make one shudder.” God had seen it; therefore man could not deny it. In the sight of God, and amid the sense of His presence, all excuses fail.

In the house of Israel - “For what more horrible, more amazing than that this happened, not in any ordinary nation but ‘in the house of Israel,’ in the people of God, in the portion of the Lord, as Moses said, the Lord’s portion is His people, Jacob is the lot of His inheritance? In another nation, idolatry was error. In Israel, which had the knowledge of the one true God and had received the law, it was horror.”

There is the whoredom of Ephraim, widespread, over the whole land, wherever the house of Ephraim was, through the whole kingdom of the ten tribes, there was its spiritual adultery and defilement.