Of whom hast thou been afraid? Judah's abandonment of Jehovah and devotion to new deities was caused by fear—the fear of man, especially of Assyria. This induced them to seek for help in each new superstition that presented itself, and produced the enlarged syncretism which has been noticed in the comment on Isaiah 57:8.
But how absurd to be driven by fear of man into offending God! That thou hast lied (see the last clause of Isaiah 57:4, with the comment). Have not I held my peace, etc.? i.e. "Is it not because I have for so long a time held my peace, that thou fearest me not?"
God had for a long time suffered them to "go on still in their wickedness"—he had not interposed with any severe judgment; therefore they had ceased to fear him, and had feared men instead.