This advance notice reveals that it is plain to the narrator that the Lord is sovereign of history, and has therefore planted this dream in the Midianite’s mind, specifically for the purpose of bolstering Gideon’s spirit. At the same time, it is appropriate that, if he is to communicate with Gideon through this pagan, the message should come in the form of a dream. Only in exceptional cases (such as Balaam, Numbers 22:1 – 24:25) did he communicate to non-Israelites through visions or oracles. But with outsiders the preferred medium of revelation was the dream.
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11 And you shall hear what they say, and afterward your hands shall be strengthened to go down against the camp.” Then he went down with Purah his servant to the outposts of the armed men who were in the camp.