RobH_en_tn/hos/05/05.md

Yahweh is talking about Israel.

The pride of Israel testifies against him

This means that the people of Israel have become proud. They do not feel the need to rely on Yahweh for anything. Their actions show their pride and arrogance ("their actions testify against them"). (See: rc://en/ta/man/translate/figs-personification)

so Israel and Ephraim will stumble in their guilt; and Judah also will stumble with them

All of the nation of Israel (both northern and southern kingdoms) will fall away from Yahweh ("stumble spiritually") because of their sin of idol worship. (See: rc://en/ta/man/translate/figs-metaphor)

They were unfaithful to Yahweh, for they have borne illegitimate children

Israel left Yahweh and worshiped idols. In their spiritual adultery, spiritual children were born who did not worship Yahweh.

Now the new moon festivals will devour them with their fields

(UDB) This means that Yahweh's judgment will come upon them. (See: rc://en/ta/man/translate/figs-personification)