Psalm 82 and biblical themes of God's sanctifying and sending agents provide the immediate argumentative background.
Psalm 82:6 is the direct citation.
Jesus' conclusion is not 'I am merely one of many gods.' He returns to his unique Sonship and mutual indwelling with the Father.
The mutual-indwelling claim intensifies rather than dissolves the unique relationship expressed in John 10:30.
They again seek to arrest Jesus.