I agree that arguing Scripture with a well trained Jehovah Witness, by that I mean with a witness who is well trained in being closed minded, is often not successful.
For them, we need to demonstrate problems with the reliability of their leaders.
Another way, is to show them reasons for the truth such as the following.
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Does Hell Cease to Exist ? Answer : No
God has no reason to bring hell into nothingness. Those in hell have the goodness, from God, enabling their existence. Even in their suffering they still will to exist, so they can remain in their sin. It is good that they exist as their existence points to the glory of God.
From a worldly and misconstrued perspective suffering seems like the worst thing possible.
So, I can see how a person thinking from that false perspective would think Hell should cease to exist.
From the Christian perspective suffering is not the worst. Sin is the worst. Suffering, when united to Christ’s, becomes redemptive and good.
And pleasure is not the best.
Manifesting the glory of God is much better.
Therefore, it is good to exist and to be a manifestation of God’s glory, even while suffering. That is why it is good to be a Saint even while suffering martyrdom.
So, it makes sense, that in His mercy God allows them, or gives them eternal existence.
God creates.
Therefore, there is no cause for Him to un-create, or to bring to non-existence, that which He has created.
God doesn’t make mistakes.
John
(I suppose that those who really wanted know, and clicked on my link above know that I did not reference Mark 9:46 NAB.
I was making a reference to Mark 9:46 in the Douay Rheims which corresponds to Mark 9:47 in NAB as a place to begin reading, but my real emphasis was on “f” - the following verse - which is highlighted if you check it out. My ability to post from my phone, as the original was done, has severe limitations.)