I'm not sure there is a singular answer to why that is the case---but I sense it might have something to do with the fact it's the first time we truly see into Shane and Oliver's hearts-unfiltered, unobstructed and, in some ways, completely uncensored.
You see, the vault itself is a physical representation of their hearts. Locked for one reason or another over the course of the series, reading Jonathan and Katherine's letters gave Shane and Oliver an opportunity to begin evaluating and exploring their own hearts, and the content therein, embodied by the flashbacks throughout their time in the vault.
Why It Worked
For one thing, they were in an enclosed space and unable to leave. Nothing to make you deal with yourself, or a situation, more effectively than an inability to walk away from it and/or a lack of distractions---because things got real once Jason took his nap, not to mention there was no cell service or internet, ensuring only good, old fashioned detective work on Norman’s part when the time was right could get them out.
Perhaps the more pressing issue, however, was the fact that, at the time, Shane and Oliver believed they only had about four hours, twenty minutes of air left to breathe. More than being in an enclosed space, suddenly only having so long left to live provided, as Oliver so astutely observed, “a certain clarity.” And that “clarity” paved the way for the pair to start doing some serious, though perhaps unintentional, reflecting.
Remember that while filming “Something Good,” Kristin got a full sense of the depth of Shane’s feelings for Oliver, which she described as an “I’m so in love with this man, [and] I-will-die-if-I-can’t-be-with-him sort of moment." Also in that episode, Shane revealed to Becky that she was sweet on Oliver without actually saying it, and was promptly reminded he was unavailable. The feelings strong, but his marriage very much a factor, Shane's true feelings for Oliver had to remain "on lockdown."
By the time they ended up in the vault, Shane and Oliver had not only developed a successful rhythm working as colleagues, but a rhythm when it came to their friendship, one that weathered both canceled dance classes and breached privacy without being destroyed. At the core of these conflicts, of course, was the reality of Oliver’s estranged wife, Holly, and the tension of Shane and Oliver’s undeniable, but undefined, connection that defied articulation by either party.
But it didn’t have to be articulated to be a reality all its own. And that’s what the core of Shane and Oliver’s interaction inside the vault revealed as they internalized and reacted to Jonathan and Katherine bearing their souls to each other on paper.
A Space Explored
“...and everything old became new once again…”
“...I am a great believer in the power of a letter to remind us what lasts…”
“All mankind can build with steel and glass and stone can never compare to a life built on love for another, and a belief in something greater than oneself…”
“...And even if we can’t keep dancing, I would like to keep that conversation going…”
Here we get an early sense of Shane’s evolving appreciation for “what lasts.” Suddenly Oliver’s embodiment of a classic gentleman, his faith and his values something “old [becoming] new once again.” Her emerging desire for the intangible things that endure and enrich our lives, like faith, are the substance of the conversation she’d like to “keep going,” in addition to, of course, a future of “dancing”---in all its connotations---with Oliver. All of these desires sit at the core of her true character, revealed and developed as the series continued, the glimpses of which are illustrated here by the moments recalled to her mind.
“...All I could imagine was you sitting next me, making jokes and singing along with the band…”
“And I am every day inspired by the everyday heroes who take up bat and ball and swing for the stars. Perhaps someday I will know the joy of standing with you as we cheer on the Tigers or the Cardinals or my beloved Red Sox…”
“There is nothing crazy about falling in love, even when…
something tells you against all common sense that you have found the one you’ve been waiting for all your life...
...all my life. And then I let you go…
...why did I let you go?
...why did I let you go?”
Neither knew what the other thought or imagined as the letters were read, yet their thoughts naturally gravitated to moments spent with each other. As they took the journey of Jonathan and Katherine getting to know each other, Shane and Oliver recalled their journey of working together delivering letters.
Yet as Katherine’s letter turned more intimate and personal, towards “falling in love with a stranger,” the tone and energy of Shane and Oliver’s reading slowed to some extent, and their memories and words merged as they reflected on the very same moment in time, colliding in some respects with Jonathan and Katherine’s realization of having fallen in love.
I would like to posit that gravity came from the acute awareness of the deepest, unexpressed desires of their heart colliding with the very present tension of Oliver being married, and the undeniable, undefined connection between him and Shane. It was more than the seemingly missed connection between Jonathan and Katherine, but a deep recognition of a space in their hearts they couldn’t access mentally or emotionally yet.
The Last Letters
It’s important that Oliver tried to reclaim the moment by continuing to read Jonathan’s letter, his tone and emphasis recapturing Shane’s imagination. Because where Jonathan and Katherine were in their romance was beyond where Shane and Oliver were, however, there were no memories to accompany this reading. In some ways it felt like Shane and Oliver met each other in a new way in this moment, living vicariously even through Jonathan’s proposal, their own fate in the vault still unknown.
But as the letter took a turn for the tragic, the reality of Jonathan and Katherine’s unfulfilled dream struck a deep cord with Oliver, whose heart seemed to sink at Katherine’s “yes, I will be your wife. Maybe not in this life, but in your heart,” as well as Shane, who descended into tears as the unknowns of both pairs left her heartbroken and, admittedly, scared. Oliver, of course, quick to comfort and calm her the best he could.
A Space Exited?
With the truth that they weren't in fact, in mortal danger, Jason awakened from his nap, and help on the way, Shane and Oliver incrementally turned their attention away from their hearts and back to reality. Perhaps the most painful realization of that fact came with Shane's declaration to Oliver, "you forgot this," handing him the letter to Holly that had, interestingly, fallen from his left breast pocket (right over his heart). As we've discussed before, this was the same moment he spoke a new phase of his relationship with Shane into being by referring to her as "lady" allowing her to exit the vault first.
Oliver took one last look inside before exiting, but the remnants of his time in the vault remained. The first instance was when asked "what was in the box," to which Oliver immediately responded, "Love, Norman, lots of love." But perhaps most directly when, on the Walker's porch the next day he advised them to "read [the letters] out loud---together," Shane and Oliver sharing a look that wordlessly spoke volumes.
Similarly, Shane pressed into faith to some extent after her time in the vault, not only in asking Oliver to pray in the vault, but once more when Rita needed to remember the thirteenth approved mode of mail transport.
The pair may have exited the vault, but it's clear the experience, and the truths of their hearts revealed inside, began immediately transforming Oliver and Shane's perspectives and demeanor.
A metaphor for the state of their hearts at the time, the vault, like their hearts, contained a lot of love that, while kept in a safe place, was still locked inside. Free of distraction, and in spite of---or perhaps even because of---the seemingly life or death circumstances, Shane and Oliver's experience in the vault initiated the process of unlocking their hearts. For Shane that meant realizing her desire for things that endure like faith, letters and love. For Oliver that meant recognizing the new possibilities laid out before him waiting to be embraced if he only had the courage, and clarity, to pursue them. While it took time for their desires to come to fruition, the process started with their time in the vault.
All of this to say that I think we're still falling in love with The Treasure Box because there is something timeless about the pursuit of our true selves, and being reminded of what "our heart[s] remember that our mind[s] [sometime] forgets" as we walk the often difficult path of life. Putting pen to paper has the power to do so, but so does the reality that "life is short" and we shouldn't waste a second of it. Besides, we never know what beautiful things our hearts contain unless we endeavor to look a little closer.
Taking Another Look,