That's not Amazon's MO, or goal with the Whole Foods purchase. They want to dominate the grocery industry like they dominate the durable goods industry.
Actually Amazon isn't always the lowest price or the best selection; their #1 aim is to try to be the most convenient (where cost is an important, but not exclusive, factor in "convenience"). In fact they differentiate prices to different consumers and ramp up prices in some popular items when they think they can increase margin. (Not that there's anything necessarily nefarious about that). They do try to make it hard to compare prices, which other retailers do as well.
> [n]or goal with the Whole Foods purchase.
We don't know Amazon's goal with the purchase. There can be several, possibly even competing ones (launch a couple, see what fly). For example they have Echo in the store: it can be just a way to switch people to online ordering and/or a way to see if people buy non-food products through this real estate they already purchased (this is how Fry's transitioned from a grocery store to an electronics store in California) and/or a way to link in-shop shoppers to their online history and/or something we don't even know about -- or they haven't thought of yet.
My money is on Amazon doing what they have always done: compete with wide selections and the cheapest pricing possible while using Whole Foods to bring their Fresh delivery service to far more markets at a higher efficiency.
I would have done this with Peapod etc but their website was lacking in 1) choices (Amazon will get you pretty much any food item) and 2) delivery window and 3) unattended delivery