Hosea 7:9

‘Strangers have devoured his strength,

And he does not know it.

Ephraim's vulnerable situation is underlined by the fact that it has lost its wealth to the nations, either by tribute, bribes or treaty presents. Contact with foreigners has not been good for their wealth. And yet the sad thing is that they are in such a sad state that they do not realise it. (Not many would have had access to the now empty treasury in order to discover the true state of things). They are still hopeful that things will turn out all right.

Yes, grey hairs are here and there on him (or ‘steal up on him'),

And he does not know it.'

The verb in the first line usually means ‘sprinkled' thus possibly indicating that they now have a sprinkling of grey hair. But based on an Arabic word the verb may also mean ‘steal up on', which would indicate that they had grown grey without realising it. The suggestion then would be that they had become old and decrepit. Others see the grey hairs as referring to the grey hairs which can be seen on mould, the idea being that they have become mouldy.

Notice the repetition of the words, ‘and he does not know it', doubly emphasising the fact. They are just totally unaware of what they are doing to themselves.