I've found it interesting how you've continued to use more modern translations instead of the KJV, but that's a conversation for another thread.
I use English bibles that are approved for use by Catholics. Sometimes I will quote from the KJV or some other Protestant produced translation that is not approved for use by Catholics but that is an exception rather than the rule. In this case the KJV has taken an approach to the passage that is incorrect. It may be somewhat justifiable in some ways but it is not especially well done so I prefer not to use it in this case. The NRSV seems better. It reads thus:
Now if people say to you, 'Consult the ghosts and the familiar spirits that chirp and mutter; should not a people consult their gods, the dead on behalf of the living, for teaching and for instruction?' surely, those who speak like this will have no dawn! (Isaiah 8:19-20)
This isn't a condemnation against necromancy as much as it is a condemnation against those who try to communicate with the dead altogether. So you're not out of the woods yet sir.
Thank you for your expressed concern but I am not in the woods.
And are you really willing to say that verse 20 has no application outside of dealing with those who speak to the dead? Do you really think you wouldn't be able to tell those who have light in them by testing what they say against the law and the testimony?
Now here I was thinking that you were concerned for the truth as expressed in sacred scripture rather than with how one can twist and bend bible verses to make a doctrine seem 'true' when it is not. I was mistaken I think in believing that your stated purpose was the rule by which this passage would be approached and interpreted.
I ask that you consider the following text as well:
Isa 8:16 - Bind up the testimony. Seal the law among my disciples.
Well, I will look at the passage containing verse 16 of the same chapter that contains verses 19 & 20 but I think we ought to deal more fully with verses 19 & 20 before we swap to a new passage. Do you agree?
Would you say that the testimony is bound up among your church, or that the law has been sealed among you?
Bind up the testimony, seal the teaching among my disciples. I will wait for the LORD, who is hiding his face from the house of Jacob, and I will hope in him. See, I and the children whom the LORD has given me are
signs and portents in Israel from the LORD of hosts, who dwells on Mount Zion. (Isaiah 8:16-18)
Bind
seal
among my disciples: because the prophets message was not well received at the time, he wanted to preserve it until the future had vindicated him as Gods true prophet (cf. 30:89).
Signs: in the meantime, while awaiting the vindication of his message, Isaiah and his children with their symbolic names stood as a reminder of Gods message to Israel.
We can return to these verses when we finish with verses 19 & 20
God keep us in the faith of the apostles.