The Lord’s mercy is said to last forever 26 times in Psalm 136. If so, what are we to do with the doctrine of eternal torment in hell, or eternal separation from God?
God has revealed Himself in Nature, as well as in the Bible. He deals with sin in perfect righteousness, not with cruel and unusual punishment.
"The heavens are telling of the glory of God; And their expanse is declaring the work of His hands...For since the creation of the world God's invisible qualities, His eternal power and divine nature, have been clearly seen, being understood from His workmanship, so that humanity is without excuse." (Psalm 19:1; Romans 1:20)
The doctrine of eternal conscious torment is a “destructive heresy" "secretly" introduced by "false teachers"...
"...false prophets also arose among the people, just as there will also be false teachers among you, who will secretly introduce destructive heresies..." (2 Peter 2:1)
Our loving and merciful Father God is just (right) in disciplining His sinful children - but has reconciled them to Himself through the blood of Christ Jesus as the Bible teaches...
“…and through Him to reconcile all things to Himself -- having made peace through the blood of His cross -- through Him, whether the things upon the earth, whether the things in the heavens.” (Colossians 1:20)
God "disciplines" His children along the way to His goal of reconciling all things to Himself. That discipline is just and in line with His Love, Grace, and Mercy.
"For the LORD disciplines those He loves, and He punishes each one He accepts as His child.” (Hebrews 12:6)
What about the Satan...and some of you reading this might as well go outside and pick up a few choice stones because I am fixing to drive you over the edge. The Bible says God will reconcile "ALL things to Himself” which must include all “things upon the earth or the things IN THE HEAVENS”. That covers all of God's creation. So, even Satan and his followers will be reconciled to God by the blood of Christ Jesus.
The "blood of His cross" is far more powerful than the religions of humanity are willing to admit.