| Barnes' Notes on the Bible 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 - o: "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.
Clarke's Commentary on the BibleI have seen a horrible thing - That is, the idolatry that prevailed in Israel to such a degree that the whole land was defiled.
Gill's Exposition of the Entire BibleI have seen an horrible thing in the house of Israel,.... Idolatry, the calves set up at Dan and Bethel, which God saw with abhorrence and detestation; or the prophet saw it, and it made his hair stand on end as it were, as the word (g) signifies, that such wickedness should be committed by a professing people: there is the whoredom of Ephraim; in the house of Israel is the whoredom of Jeroboam, who was of the tribe of Ephraim, and caused Israel to sin, to go a whoring after idols; or the whoredom of the tribe of Ephraim, which belonged to the house of Israel, and even of all the ten tribes; both corporeal and spiritual whoredom, or idolatry, are here meant: Israel is defiled; with whoredom of both kinds; it had spread itself all over the ten tribes; they were all infected with it, and polluted by it; see Hosea 5:3. (g) a "pilus".
Geneva Study BibleI have seen an horrible thing in the house of Israel: there is the whoredom of Ephraim, Israel is defiled.
Wesley's Notes 6:10 The whoredom - Idolatry. Of Ephraim - Which was brought in by an Ephraimite, by Jeroboam, two hundred years ago, and is there still. Israel is defiled - It hath overspread all Israel.
Jamieson-Fausset-Brown Bible Commentary10. horrible thing-(Jer 5:30; 18:13; 23:14). whoredom-idolatry.
Matthew Henry's Concise Commentary6:4-11 Sometimes Israel and Judah seemed disposed to repent under their sufferings, but their goodness vanished like the empty morning cloud, and the early dew, and they were as vile as ever. Therefore the Lord sent awful messages by the prophets. The word of God will be the death either of the sin or of the sinner. God desired mercy rather than sacrifice, and that knowledge of him which produces holy fear and love. This exposes the folly of those who trust in outward observances, to make up for their want of love to God and man. As Adam broke the covenant of God in paradise, so Israel had broken his national covenant, notwithstanding all the favours they received. Judah also was ripe for Divine judgments. May the Lord put his fear into our hearts, and set up his kingdom within us, and never leave us to ourselves, nor suffer us to be overcome by temptation. | 
