“the new moon will devour them.” In astronomy, the “new moon” is the time when the moon cannot be seen from earth, and the sky is dark. But biblically, the “new moon” is when the first sliver of the moon can be seen, and when it was seen, and the sighting was verified by other witnesses, the new month began on the Jewish calendar and the Jews held a festival to celebrate.
The phrase “the new moon will devour them” here in Hosea 5:7 is a reference to the fact that the Israelites had mixed their pagan worship into the worship of God, and so their new moon festivals had become pagan and evil (Isa. 1:13-14. Cp. Neh. 10:33; Ps. 81:3; Jer. 8:2; Ezek. 46:6). Now the consequences of their sin were about to come upon them, and they were about to be destroyed because of their ungodly ways.