A strong argument for Universalism comes from considering the state of eternal bliss of those who are in heaven.
Revelation 21:4, “and He will wipe away every tear from their eyes; and there will no longer be any death; there will no longer be any mourning, or crying, or pain; the first things have passed away.”
The argument questions how one can be eternally blissful in heaven if sorrow springs from realizing that not all others are there, especially considering the admonition of Jesus to love our neighbor as ourselves (Matthew 22:39). The argument concludes–from the apparent contradiction that would exist between eternal heavenly bliss and earthly memories of loved ones missing in heaven–that all eventually end up in heaven.
A common critical response by those not in the Universalism camp–I’ve even seen it here in this forum–is we won’t have those earthly memories in heaven, as supported by Isaiah 65:17: “For behold, I create new heavens and a new earth; and the former things will not be remembered or come to mind." But this is a clear example of the dangers of taking a verse out of context. When context is provided by just the previous verse, i.e., Isaiah 65:16, such a conclusion is not warranted: “Because he who is blessed in the earth will be blessed by the God of truth; and he who swears in the earth will swear by the God of truth; because the former troubles are forgotten, and because they are hidden from My sight!” Verse 16 is specifically speaking of God forgetting, i.e., “because the former troubles are forgotten, and because they are hidden from My sight.” And verse 17 is likely to be simply continuing this theme. There is a biblical precedent for this forgetting being applied to God, as Jeremiah 31:34 establishes, “for I will forgive their iniquity, and their sin I will remember no more.” (Further, God is not really forgetting in the sense that He no longer can remember; it’s that He will not bring these things to mind in holding them against us.)
But there is no biblical precedent for such forgetting being applied to humans. To the contrary, there is clear indication that earthly memories are retained in heaven. For example, consider 2 Samuel 12:23. “But now that he is dead, why should I fast? Can I bring him back again? I will go to him, but he will not return to me." David said he would go to his son. Clearly, David assumes he will carry with him memory of his son in heaven.
Also, consider 1 Corinthians 13: 9-12, which seem to show memories are retained when the perfect comes. “For we know in part and we prophesy in part but when the perfect comes, the partial will be done away. When I was a child, I used to speak like a child, think like a child, reason like a child; when I became a man, I did away with childish things. For now we see in a mirror dimly, but then face to face; now I know in part, but then I will know fully just as I also have been fully known.” That last statement, “but then I will know fully just as I also have been known fully” indicates that we shall know others as well as be known by others when the perfect (i.e., heaven) comes.
Given that Isaiah 65:17 most likely applies only to God and that the Bible mentions humans who do retain their earthly memories in heaven, as documented above, the application of Isaiah 65:17 to human memory is problematic at best.