Because he had been commanded to offer sacrifice upon the rock where the Angel appeared to him, Gideon concluded that 556 he had been appointed to officiate as a priest. Without waiting for the divine sanction, he determined to provide a suitable place, and to institute a system of worship similar to that carried on at the tabernacle. With the strong popular feeling in his favor he found no difficulty in carrying out his plan. At his request all the earrings of gold taken from the Midianites were given him as his share of the spoil. The people also collected many other costly materials, together with the richly adorned garments of the princes of Midian. From the material thus furnished, Gideon constructed an ephod and a breastplate, in imitation of those worn by the high priest. His course proved a snare to himself and his family, as well as to Israel. The unauthorized worship led many of the people finally to forsake the Lord altogether, to serve idols. After Gideon's death great numbers, among whom were his own family, joined in this apostasy. The people were led away from God by the very man who had once overthrown their idolatry.

Gideon havde fået befaling om at bringe et offer på den klippe, hvor engelen viste sig for ham, og nu troede han, at han var blevet udset til at gøre præstetjeneste. Uden at vente på guddommelig godkendelse besluttede han at finde et egnet sted og at indføre et offersystem i lighed med det, der fandtes ved tabernaklet. På grund af den store popularitet, han nød i befolkningen, havde han ikke svært ved at gennemføre sin plan. På hans anmodning gav folket ham alle de guldørenringe, de havde taget fra midjanitterne, som hans andel i byttet. Folket skaffede også mange andre kostbarheder til veje, blandt andet de midjanitiske fyrsters rigt udsmykkede klæder. Gideon benyttede disse materialer til at lave en efod og et brystskjold af samme slags, som ypperstepræsten bar. Dette blev en snare både for ham selv, hans familie og for Israel. Mange af israelitterne forkastede til sidst Herren fuldstændig på grund af denne selvbestaltede gudsdyrkelse og begyndte at tilbede afguder. Efter Gideons død tog store skarer del i dette frafald, deriblandt hans egen familie. Folket blev ført bort fra Gud af den selv samme mand, der en gang havde bekæmpet afgudsdyrkelsen iblandt dem.