One of the purposes of the book of Hosea was to highlight what issue within Israel?

The book of Hosea addresses the theme of spiritual adultery primarily through the metaphor of marital unfaithfulness. Hosea himself experiences a personal tragedy as his wife Gomer is unfaithful to him, which serves as a poignant illustration of Israel's relationship with God. This imagery emphasizes how the people of Israel have turned away from their covenant with Yahweh, seeking after other gods and engaging in idolatry. The prophet uses this personal experience to challenge the nation to recognize their own unfaithfulness and the consequences that arise from it. Thus, the book serves as a call for repentance and a return to faithfulness to God, highlighting the severity and implications of Israel's spiritual infidelity.

In this context, while betrayal and rebellion, social injustice, and false prophecy are relevant themes within the broader prophetic literature, the specific emphasis in Hosea is on spiritual adultery as it encapsulates the essence of Israel's waywardness from God.