‘Ephraim feeds on wind, and pursues the east wind, he continually multiplies lies and desolation, and they make a covenant with Assyria, and oil is carried into Egypt.'
To feed on wind is to feed on what is insubstantial. The idea is that Ephraim, instead of feeding on the Law of God, had rather chosen to follow lies. To pursue the east wind is to pursue the scorching desert wind which sweeps in from the east, a symbol of judgment and desolation. Before the east wind nothing lives, who then with any modicum of intelligence would pursue it? The indication therefore is that, without realising it, Ephraim were foolishly pursuing the course that would lead to desolation.
And they did both in no half measure. They ‘multiplied' lies and desolation (the idea of multiplying was a favourite of Hosea's - see Hosea 4:7; Hosea 8:11; Hosea 8:14; Hosea 10:1; Hosea 10:13). The lies included all the religious deceit whereby they pretended to be worshipping YHWH but were in fact worshipping Baal and Asherah. One way in which this attitude of heart came out lay in the fact that they had first made a covenant with Assyria (2 Kings 17:3). This had only been necessary because they had forsaken YHWH and had followed their false gods. But it had been compounded by the fact that they had then broken their treaty by carrying olive oil to Egypt (2 Kings 17:4).
The thought in the latter was not that they were trading with Egypt, for that would have been permissible, but that they were taking presents to the king of Egypt in order to obtain his backing in a rebellion against Assyria. They were thus doubly treacherous. Had they looked to YHWH there would have been no need for a vassal treaty with Assyria, as Isaiah would point out to Ahaz in Judah (Isaiah 7:1-11). Thus by looking to Assyria they were openly rejecting YHWH. But once having made a sacred treaty with Assyria, to deceitfully go behind their backs and seek assistance from Egypt (see 2 Kings 17:4) was to indulge in double treachery and deceit, and was to court desolation. It was a double rejection of YHWH, for it indicated that in seeking deliverance from Assyria (something that the Deliverer from Egypt was good at if only they would realise it), they instead sought help from Egypt. It was a double whammy.