Wow, tpe, how to narrow it down to just 2 or 3 important scenes?? Big dilemma, I don't envy you that task!
Personally, IMHO, I would say at the very least the "prayer of Thanks" scene, because it lays out Jack's desire for their future and the fears that control Ennis's life, fears that inevitably prevent Jack's dreams from coming to pass. The next 16 years are more or less laid out from this point, perhaps??
Maybe the divorce misunderstanding scene, because it represents the gut-shot to Jack that starts the slow, painful death of the hopes he'd been holding on to in spite of Ennis's earlier assertions that it was not to be.
That scene then ties into the final confrontation they have at the river on their last camping trip, the "I wish I knew how to quit you" scene. Here are the ashes of lives not lived and raw wounds are finally laid bare to each other.
Of course, a scene from their Brokeback summer would be rquired maybe to show the growth of their friendship and love ... but what scene would you choose there, out of all of those beautiful moments, to represent the birth of their relationship??
Just my 2 cents, "for what it's worth".
