Isaiah 66:4
I also will choose their delusions, and will bring their fears upon them; because when I called, none did answer; when I spake, they did not hear: but they did evil before mine eyes, and chose that in which I delighted not. I also will choose their delusions, and will bring their fears upon them; because when I called, none did answer; when I spake, they did not hear: but they did evil before mine eyes, and chose that in which I delighted not.
Isaiah 66:4 describes people who have had great light yet have chosen their own ways and delighted in abominations, who are not afflicted and astonished at their moral and spiritual condition. Their guilt is that when God called they gave no answer and when He spoke they would not listen. They reject His warnings and refuse to hear His call.
In response God chooses their delusions and brings their fears upon them. They are left to the delusions they themselves have chosen, and the fears they bring on themselves follow their rejection of God. The chosen delusion is believing a lie, because they received not the love of the truth that they might be saved but had pleasure in unrighteousness.
In its strongest form that delusion is the pretense of building on the right foundation and that God accepts their works. In reality they work out many things on worldly policy and sin against the law of Jehovah which guards the interests of every being for whom Christ gave His life. They mistake the form of godliness for the spirit and power thereof, and suppose themselves rich and increased with goods and in need of nothing when they are poor and in need of everything.