This is a bit more open-ended than usual, but there's no one else I could ask. To wit: are there any particular moments in Series 4 that suggest or demonstrate to you that John really loves and/or genuinely cares about Sherlock? I guess secondarily, how do you read Sherlock putting off rescuing John from that well until after he dealt with Eurus In TFP?
Any particular moments? It’s hard to pick, it’s kind of infused through the whole thing, but okay, I’ll do my best.
In The Six Thatchers, John should be deliriously happy. He’s got what he wanted: the normal life with a job, a wife, and a new daughter, but he’s also got Sherlock, who is as committed to maintaining this careful and potentially awkward balance as he is. They still solve crimes together, and Mary and Rosie aren’t an obstruction. In fact, sometimes they join in! John’s devotion to Sherlock is pretty obvious from that alone, but Sherlock’s special place in John’s life is underscored by John asking him to be Rosie’s godfather.
John should be happy, but he’s not. He’s never managed to get over what Mary did and who she really is. His happy life with wife and baby is a lie. As his trust in Mary continues to decline, his trust in Sherlock never waivers. John and Sherlock confront threats together as a team while Mary lies, drugs Sherlock, and scarpers. Sherlock, weird, rude, and difficult, is John’s stable rock, and Mary does not look good in comparison.
After Mary dies, John blames Sherlock and cuts him off. I’d suggest that this is more indicative of how much John cares about Sherlock than otherwise. Not only because he thought Sherlock was a superhero who could could genuinely protect Mary and Rosie from everything forever, but because, as we later learn, the reason why John pushes Sherlock away stems primarily from his own self-loathing. John betrayed Mary, and his guilt and despair at not being able to live up to Mary’s, Sherlock’s, and his own expectations leads him to push away the things he loves most, including his daughter and his life with Sherlock. This is underscored by his goodbye scene in the hospital, where he leaves his cane as a silent final message: you saved me, I didn’t deserve it, and here I betray you.
We’ve had Sherlock’s mind palace for a while, which is a wonderful way to see what’s actually going on in his head. In The Lying Detective, we finally get the equivalent for John: Mary. Hallucinated Mary isn’t a ghost or even a memory, she’s the honest part of John. And she adores Sherlock. She talks about him constantly. She watches him mid-deduction with love and delight. She recognizes that Sherlock knows John, understands him completely, but John disagrees. Sherlock can’t possibly know how worthless John is; like Mary, Sherlock believes he is a good, moral man, and John knows that they’re both wrong. The voice in his head says: Sherlock may be a monster, but he’s my monster.
The most dramatic indicator of how John feels about Sherlock is his confession and breakdown at the end of The Lying Detective. This is the first time John has been completely honest in this entire story. John hides his feelings constantly, he lies about them, even to himself. And in this scene he nearly does it again, he nearly walks away. Had he done so, I believe his relationship with Sherlock would have been essentially over. He would have grown more and more distant and dishonest until their connection was entirely lost. But out of love and faith, he finally, finally makes a different choice. He chooses to be brutally honest and vulnerable. He cries, but does not turn away. He lets Sherlock hold him. No one has or ever will be this close to John.
Sherlock does not put off rescuing John in The Final Problem. From the moment he realizes that John is in danger, all Sherlock does is try to save him. The problem is that the solution is Eurus. We know that he can’t rescue John without her intervention because he was unable to the first time; the puzzle is too complex for him, it will always be too complex for him. The mistake he made all his life was thinking that intelligence was the answer. When he was a boy he didn’t have the resources to do what he does now: he recognizes that it’s sentiment that will save John, not brainpower. He’s got sentiment in his tool belt now, and that’s because of John. John made him feel and taught him to be a loving and feeling person, and that’s what allows him to triumph over his much more brilliant sister in the end.