This might be the best explanation of Season 3 I’ve come across. It was just a comment beneath a YouTube video (https://www.youtube.com/watch?v=FPTfaQu5Ju8) by a user named Just Some Guy. Let me know what you think...

Here are my two cents. A recurring theme of TP is the duality and balance of nature and existence: Light and Darkness, Ying and Yang, White and Black, Lodge. On Earth, this balance was disrupted when the A-bomb went off in the Nevada desert in '45 thus causing an inter-dimensional rift to open and release the ethereal demons of Judy, Bob, Mike and the woodsmen who look like Abe Lincoln, among others, into our realm. As a response to this, the Fireman, sent a good, ethereal spirit to counterbalance the evil forces which were released into our world through a gnossis sphere (a deus ex machina-like device). I believe that Laura Palmer, Carrie Page, and even Maddy Ferguson were created in that benevolent spiritual being's image- like humans were supposed to be created in the image of God. Remember, in Ep. 8 the Fireman sends the Laura looking entity/spirit directly after the events of the A-bomb explosion and the release of the demons in Nevada.

In effect, Laura, Maddy and Carrie Page were tulpas of the Laura entity. As explained in the series, tulpa's are thoughtform creations, created by two or more entities. Tulpas, however, seem to be yanked from the world, once they come to the complete realization that they are NOT who they seem to be. That's what happened with tulpa Diane; she realized that she was a copy and that she was imminently going to be ripped from reality. Thus, she probably pulled out the gun to shoot herself (not Gordon and Albert). The effect of being ripped or torn from reality is horrifying and painful: like being about to be killed in a dream state and then waking up from that nightmare screaming, thus, the whole reference in the Monica Bellucci dream about the dreame’s dreaming and the question about who really is the dreamer. This would also jive with what happened to Audrey as the real Audrey probably woke up in a hospital soon after her tulpa sprang the mortal coil. The real Audrey was most likely in a coma from the bomb explosion in the bank 25 years ago. This would also be consistent with the shocked look in Audrey face when she looked at herself in the mirror. She was also wearing a hospital like gown and was in a white room. Bad Coop and some other demons most likely made the tulpa to replace Audrey. I think the main victim, Laura was probably a tulpa too given the fact that she tells James in FWWM that she is not herself and that real Laura was gone long ago.

Regarding the Black Lodge, time is non-linear and doesn't exist in such a fashion in the Lodges- as it does in our world-hence the one armed man's question, "is this the future or the past?" Given this set up, here's what I think happened: the real coop indirectly caused Laura Palmer's murder as well a time loop in Twin Peaks when he went back in time. Indeed, in FWWM, when Laura and James stop in the middle of the woods and talk and Laura looks over James's shoulder across the woods, she screams.But in the movie itself we don't see what she sees- it's left up to the imagination of the viewer. However, in TP3, we see that Agent Cooper is standing behind some trees and bushes staring at her. In the FWWM version, Laura screams and is frightened by what she doesn't understand -- namely, the FBI agent from her dreams and the person whom Annie referred to, is standing across the woods from her. This fear causes her to react by withdrawing to the company of Leo, Jacques, and Ronette for sex, drugs and alcohol which we know ultimately leads to the clutches of Bob, who has possessed Leland. In the TP3 version, Laura makes the alternate and active decision to face her fear and take Coop's hand, which in turn, erases the events leading to her fate. But remember, it's Laura's death that also leads her soul or essence to be trapped in the Black Lodge as well. Since, she is no longer in the BL and since time has no meaning in the BL (at least not the way that we know it), not only does Laura's corpse disappear in Ep. 17, but she is also yanked or torn from the BL in S 03 ep 02. Here's where the analysis gets a bit tricky:the demons that were released way back in '45 (namely Bob and Judy) congregated to TP, Washington because it was a hotbed of spiritual activity. Moreover, they went to the BL (which is not evil by itself per se) in order to gain power and information. I think this is where they gained the knowledge of the existence of the Laura entity which was sent to counterbalance them. Mind you, time is not linear in the BL realm and there is a time loop in TP . And, so Judy and Bob created a birth-like tulpa in Laura Palmer. First, Judy entered young Sarah Palmer's mouth via a bug in '56 and laid dormant inside her. And then, Bob gradually entered into a young Leland Palmer. Sarah and Leland got married and Sarah had Laura Palmer (who is a tulpa of the benevolent Laura entity). S and L sought to use the tulpa to assimilate and corrupt the good Laura entity.

Nonetheless, when Laura chose to go with Coop in Ep 17 instead of going to Leo and gang, the time loop in the TP world was broken. Since Laura never got murdered and never put on the ring which sent her soul or spiritual essence to the BL- Judy and the demons not only lost access to the Laura tulpa, but they also lost the information leading to their awareness of the Laura entity. Judy became aware that she was losing the tulpa and thus any possible opportunity to corrupt the Laura entity so that's why she grabbed the picture with image of Laura and started smashing it. But, without an awareness of who the Laura entity is, the tulpa as a device to gain access to the Laura entity became obsolete so that's why Laura Palmer was ripped from the hands of Coop as they were traveling in the woods. Thus, in effect, Cooper did save Laura but Coop saving her, also had the inapposite result of ripping her from their reality. But, Coop, did also create an alternate timeline by going to the past and perhaps a retroactive alternate timeline. So, without any knowledge or access to the Laura entity in the alternate timeline, and since Laura Palmer never went to the BL in the alternate timeline in the first place, Judy and Bob did not seek to cultivate her as an access device. And although Leland and Sarah did have a daughter in the alternate timeline- in the alternate world, they put her up for adoption as a baby and that she wound up in Odessa, TX with the Page family and was given the name of Carrie Page.

Finally, Coop gained an awareness that his actions created the alternate universe where Laura now may not know of who she was in the first timeline: thus, the whole reference of killing two birds with one stone- saving Laura by taking her with him to make her aware of who she really is. But, I think that Cooper himself did not know that even Carrie Page is a copy and that the only real Laura is the Laura entity itself or herself. Cooper's actions again were doomed to failure because by making Carrie aware of who she was in the other world, Carrie would also come to the sudden realization that she too was a tulpa as some hidden piece of information lay dormant within her--- which was triggered by her visit to her original house in TP. Therefore, the reference to Richard and Linda was thus a warning- Cooper was not meant to go after and save alternate universe Laura (Carrie Page) as Richard and Linda were not meant to be together as so stated in that letter.

Hope this helps.