Adam Clarke on Judges 17:5

The man Micah had a house of gods - בית אלהים beith Elohim should, I think, be translated house or temple of God; for it is very likely that both the mother and the son intended no more than a private or domestic chapel, in which they proposed to set up the worship of the true God.

Made an ephod - Perhaps the whole of this case may be stated thus: Micah built a house of God - a chapel in imitation of the sanctuary; he made a graven image representing the ark, a molten image to represent the mercy-seat, teraphim to represent the cherubim above the mercy-seat, and an ephod in imitation of the sacerdotal garments; and he consecrated one of his sons to be priest. Thus gross idolatry was not the crime of Micah; he only set up in his own house an epitome of the Divine worship as performed at Shiloh. What the teraphim were, see the note on Gen 31:19; for the ephod, see the note on Exo 25:7; and for the sacerdotal vestments in general, see the note on Exo 28:4, etc.

Who became his priest - כהן cohen, which the Targum translates chumera. The word כהן cohen is the common name in Hebrew for a priest of the true God; but sometimes it is applied to idolatrous priests. When it is to be understood in the former sense, the Targum renders it cahen; when in the latter, it uses the word כומרא chumera, by which it always understands an idolatrous priest. But that this was not a case of idolatry, and that the true God was worshipped here, is evident from the word Jehovah being used, Jdg 17:4, and oracular answers being given at this house, as we see from Jdg 18:6, etc.