Yahweh is talking about Israel.

## I know Ephraim, and Israel is not hidden from me.  ##

Yahweh knows that Ephraim (Israel) is idolatrous. There is no way that they can worship idols without Yahweh knowing what they are doing. (See: [[rc://en/ta/man/translate/figs-parallelism]])

## Ephraim, now you have become like a prostitute ##

Ephraim are being compared to a prostitute since she is so unfaithful to God (See: [[rc://en/ta/man/translate/figs-simile]])

## for the spirit of adultery is in them ##

the people of Israel are so inbred with their idolatrous practices they are not like the people of God. (See: [[rc://en/ta/man/translate/figs-metaphor]])

## and they do not know me, Yahweh ##

Israel no longer listens to or follows Yahweh in any way. They do not acknowledge him as their God.