(Gifs for TFP belonging to @livingthegifs)
Another clue that Molly is John in the “I love you” scene: she wears the stripped jumper she was wearing in TEH as she played John during Sherlock’s case. “You’re not John, you’re you” was followed by Sherlock calling Molly John throughout the entire deduction scene.
The coffin was for John, the deductions apply to him -> short size, no close family, “I love you”.
The I love you scene is about John & Sherlock: it shows John’s worries about Sherlock’s potential love: “I am not an experiment”, “You’re my friend”.
It also prepares the actual scene of the confession/declaration of love : Sherlock will have to say it first, it will be in a seemingly life-threatening situation (actual Three-Garridebs?), John will answer right away and will pour his heart out, literally wearing his heart (=phone) on his sleeve.
Except that the actual I love you scene will feel right, not like this very awkward and forced scene. John & Sherlock’s declaration of love will not be destructive, it will save the life (and their hearts).
It will repair the wrongs and heal the wounds. For the characters, but also for the audience, particularly LGBTQ+ viewers. (Hopefully, Molly will have the I love you she deserves too, from a character who actually loves her -> Greg?)