The Motion Picture is of its time. Its ambition was 2001: A Space Odyssey. Its graphics were from the first Star Wars film (A New Hope), Its costumes are horribly dated by the time. And I LOVE this movie.
Star Trek, as I said earlier, is the wonderment of what we would find in space and the prism of that imagination, used to tell the story of the internal journey, the human adventure. Kirk, Spock, and McCoy became a well-oiled machine in The Original Series. By the time of this movie, they are off their game. Kirk, obsessed with doing what he does well, is at-odds with the would-be Captain Decker. McCoy is telling him to back off or the mission will fail. Spock is disappointed and humbled by not completing the Kohlinar. He is still able to save this mission by having a connection to V'Ger and the knowledge to balance the engines, and the relationships, aboard the Enterprise.
The internal journey, in this one, is to find purpose and meaning for your life. Spock, Kirk, and V'Ger are going through the same struggle. V'Ger wants to know its God in order to find purpose. Spock is curious about V'Ger, wants peace and the clarity of logic, acceptance from himself and his society. Kirk wants the Enterprise, and the excitement of commanding a Starship. All start from a place of melancholy, because they lack purpose. That's the human adventure.
The mystery of V'Ger is fleshed out as the unknown, what we would find in space. We do not know if there is a ship at the heart of the cloud, if it is intelligent, if the crews is millions, or thousands, 100 feet high. It has tremendous power for destruction, but we don't know what it is, where it comes from, what its motivations are. We assume from the contact of Epsilon 9, that we cannot take a defensive posture, but we're taking shots in the dark. They truly are in the unknown. And the tension builds, until Ilia becomes a gateway, the manifestation, of V'Ger's voice. Otherwise, how would we communicate with it? It's a throw-back to some of my favorite Trek. The stakes are high--earth and the Enterprise itself--but we still have to enter the cloud, take the risk of destroying the Enterprise, communicate with V'Ger, try to find a way around its intentions, and complete the mission--save earth. Not a shot is fired. Outside of the Klingons launching torpedoes, we don't see a single weapon. We aren't going to overpower this enemy--it's too strong. Instead, we manipulate it. We ask it questions. We bluff. We try to get to the heart of the cloud, to unravel the mystery, and we do not kill it. We give it what it needs, and it dissipates. Kirk is back in command, Spock finds out what V'Ger is and finds his purpose fulfilled aboard the Enterprise, and they ride off into the sunset, like any great western.
This is my second favorite of the Star Trek films, all 12 of them. I would like to see them attempt another movie like this, but it probably would kill the movie series. And that just makes TMP that much more precious.