Dad & Plaid
It wasn't lost on anyone that Oliver and Papa O'Toole were perfectly paired for their USPS commercial. Oliver opts for that now iconic plaid blue suit, while dear old dad wears a matching shirt. In a way it acts as shorthand for their relationship. Joe keeps Oliver close, and Oliver, to some extent, keeps his dad at a distance, hence his representation in Oliver's outermost layer. Also on the outside, though, positioned over his heart, is a bright yellow pocket square reminiscent of the first rose of summer, or Shane.
Keep your eye on Oliver's dress shirts from here on out, though. In most cases he's rocking a plain light pastel of pale blue/purple variety and equally subtle tie. His dress shirts will act as a connection to Dale, and we'll get into why and what it means shortly.
A Fine Line
It is curious that Oliver's attire also seems split between Dale and Shane at the service. His dress shirt and pockets square hold closer connection to Dale, while his plain, dark suit connects him to Shane.
Even so, I wouldn't count Shane out. Interestingly, if you keep an eye on Oliver's suspenders, the two times he is seen without his jacket in the office they are black, and match Shane. Notice this is a layer under his jacket, but just outside his heart in a sense. She's closer, but she's not "the" reflected entity. It's still the pale shirt and, ultimately, his faith. All his associations, however, get overhauled by his journey into the wilderness.
There are several significant points to be taken away from Oliver's wilderness wardrobe. The first is how it's completely opposite of anything we've ever seen him in. Separated from the comfort and familiarity of the DLO, Oliver and his wardrobe, are thrust into new and uncomfortable emotional and spiritual territory. And no one is more aware of that fact than an admittedly "over-dressed" Oliver.
As we've discussed in the past, Oliver's suits are a form of armor, protecting him emotionally. The more layers of clothing, the more guarded his heart. So more layers than normal heading into the wilderness only emphasize the depth of his need to protect himself.
Despite enlisting the extra padding to protect himself from the wilderness, he is absolutely his most exposed and vulnerable in this space, and experiences his greatest transformation as a result of the circumstances therein as a result.
Of course it's this transformation that is on full display in Oliver's actions once he returns to civilization. Unshaven and "look[ing] terrible," Oliver is his most decisive and even vulnerable. Exiting the wilderness, Oliver's wardrobe ties to Dale are almost completely severed (their both wearing jeans), but in addition to having lost two layers, Oliver becomes intricately connected to Shane's wardrobe. The white undershirt, black and white striped shirt, and tan jacket are the same colors tightly woven into Shane's jacket. She is represented in every layer of his clothing. After being estranged both physically and in terms of wardrobe throughout the entire film, they are never more connected in this film as they are during this chapel scene.
No question being stripped of that with which Oliver was familiar provided a prime opportunity for his transformation, but it appears that being stripped of his typical "armor" was a key to facilitating that transformation as well. Doing so cleared the path for Oliver both emotionally and spiritually, allowing him to achieve a newfound clarity and once more connect with Shane.