Implied, but not detailed, in Paradisical Slices, was the utter bliss of being aware that others are suffering while you have a great Christian time. So, if you're a grandmother who loves her grandson, and he's a casual atheist but you are seriously orthodox, and you both live basically good lives and are nice to others and forgive others their trespasses against you and donate to charity or whatever, but your grandson never accepts Jesus despite his outward appearance of niceness, he's not destined for Heaven.
Being a good person, Grandma grieves for Grandson, and when she's getting an ultra pedicure and forty orgasms while eating cheesecake in Heaven's spa 500 years later, she recalls, "Oh yeah, my offspring will never reach their existential apex like me," or at least Grandson (and all of his and my descendants) never will. Her apex, her ecstasy, can't just be about her, because she's not selfish; she feels the pain, of everyone else, of a treasured child, or a cherished friend, or just a random million others who didn't know Jesus, being either tortured exquisitely in Hell or just barred forever from the sight of God, unable to remedy that mistake.
Maybe there are classes in Heaven. "Dealing With The Damnation of a Loved One." Down at the Y on 7PM Tuesday nights. This is Mitch; he's been here every night for 342 years; a thing with his wife. Yeah, it's a great program; gotta try it. Oh, take one, there's like a hundred of them, yeah, no one really reads them. Come on, it's my first time leading a session, Gabriel's watching, won't you please--ohh, thank you.
Achieving an effective salvation, then, has to mean either forgetting that such failures existed, or coming to believe that it is not only an ultimate good, but an ultimate joyous good, that others you knew about are in hell. Assuming a non-lobotomized paradise, attendees then have to be fully on board with the damnation part of the program--either they're completely careless about those endless tortures ("God handles it; that's not for such as I to decide"), or, in a more responsible, realistic way, they accept the truth and justice of those endless tortures. While some people might be 100% unaffected by that, the most giving and compassionate of Heaven's flock would likely include some who, if not lobotomized, felt a little bad about all those people eternally suffering. Maybe not someone who was unpopular when they heard about him on Earth, but someone relatively unknown, who was basically kind and sweet but had been unfairly convinced by modern culture that some rabbi 2,000 years ago hadn't died "for their sins." Considering one's imagination of what eternal torture might include, being aware of someone's lack of everlasting fulfillment, or of someone's scrotum being tasered, during one's happiest moments of fulfillment, would likely affect one's senses as to the completeness of that fulfillment.