The proximity of other deities seems to be key. The example I cite, 1 Corinthians 8:10–13, has the ‘weak’ Christian thinking the rival deity (being worshipped in the Temple) has power. So… ‘sin’ happens.

The rival deities seem to be recognized by the bad feelings they inspire. A bad deity is known through jealousy, hatred, etc., as God is love. To re-focus on love is then to ‘purify’ the evil.