Hos 5:3-4 I know Ephraim, and Israel is not hidden from me; for now, O Ephraim, you have played the whore; Israel is defiled. Their deeds do not permit them to return to their God. For the spirit of whoredom is within them, and they know not the Lord.
Samaria, the capital of the Northern Kingdom, lies in the region of Ephraim. Adam and Eve tried to hide themselves from God and could not. Cain tried to hide the murder of his brother from God and could not. Perhaps a century before Hosea gave these prophecies Jonah tried to hide from God and could not. No sin inside of Israel, even in the darkest hiding places in its capital, could be hidden from God. By referring to Ephraim rather than Samaria specifically, it seems God is speaking to the people as a whole and not merely its priests and politicians. God is declaring through Hosea that He knows they are unfaithful in their worship and practice vile sexual sin both literally and figuratively. Likewise, none can hide from God. At some point all will be judged and found lacking. Only the application of the blood of the Lamb of God can cover sins and provide merciful forgiveness. Whoever enters or otherwise remains in rebellion to God does not know Him and faces the wrath of God when judgment is applied.