Book of Hosea Chapter 5 Vs. 3

 Punishment Coming for Israel and Judah

I know Ephraim, and Israel is not hid from me: for now, O Ephraim, thou committest whoredom, and Israel is defiled. Hos. 5:3

I know Ephraim... Ephraim was the largest tribe, and the name became that of the northern kingdom, just as Judah became the name of the southern kingdom because of it being the ruling tribe (Hos. 5:3, 5:5, 5:9-15). Ephraim, the tribe so called, as distinguished from "Israel" here and the other nine tribes. It was always foremost of the tribes of the northern kingdom. For four hundred years in early history, it, with Manasseh and Benjamin, its two dependent tribes, held the pre-eminence in the whole nation. Ephraim is here addressed as foremost in idolatry.

not hid from... Not withstanding their supposed profound cunning (Hos. 5:2; Rev. 2:2, 9, 13, 19).

for now, O... Though I have been a rebuker of all them (Hos. 5:2), who commit such spiritual whoredoms, thou art now continuing in them.

Ephraim was the most prominent of the tribes of Israel. Just as many times, Judah was spoken of as both the tribe of Judah and Benjamin, and other times was separated out, so is Ephraim. It appears, Ephraim was even more idolatrous than the other tribes. They had received the right hand blessing, so perhaps they were also, more responsible.

I know Ephraim, and Israel is not hid from me-for now hast thou played the harlot, Ephraim, Israel is defiled." The worship on the high places, whether nominally of Jehovah or not, was sheer service of Ba’alim. It was in the interest both of the priesthood and of the rulers to multiply these sanctuaries, but they were only traps for the people.