Albert Barnes Commentary Hosea 5:9

"Ephraim shall become a desolation in the day of rebuke: among the tribes of Israel have I made known that which shall surely be." — Hosea 5:9 (ASV)

Ephraim shall be desolate - It shall not be lightly rebuked, nor even more grievously chastened. It shall not simply be wasted by famine, pestilence, and the sword; it shall be not simply desolate, but a desolation, one waste, in the day of rebuke, when God brings home to it its sin and punishment. Ephraim was not taken away for a time; it was never restored.

I have made known that which shall surely be - “Do not doubt that what I say shall come upon you, for it is a sure saying that I have made known;” literally, one well-grounded, as it was, in the mind, the justice, the holiness, the truth of God.

All God’s threats or promises are grounded in past experience.

So it may also be, as though God said, “Whatever I have until now promised or threatened to Israel, has come to pass. In all this I have proved Myself true. Let no one then flatter himself, as though this were uncertain, for in this, as in the rest, I shall be found to be God, faithful and true.”