This is not going to be any well-constructed essay with any kind of point - just some thoughts strung together. I will add to this as I think up new stuff.
First of all: is the Lodge one place or two? Everyone refers to 2 Lodges, the Black and the White,
but we see only one place: the Red Room. Some people say that this is merely the Waiting Room, a
place that adjoins both Lodges. I can't disprove that at all, but my feeling is that this is not
true.
First of all, in the last episode, when Cooper finds the entrance to the Black Lodge, he finds the
Red Room. When he meets his doppelganger it is in the Red Room (remember Hawk's statement
that your soul passes through the Black Lodge and meets the "Guardian on the Threshold"). Also (I don't
remember this personally, but) Windom Earle apparently spoke through someone on Earth and said that he was
in the Black Lodge when we see him only in the Red Room. (Although it's not canonical, Lynch's
Japanese Georgia Coffee commercials tell us that the Red Room is in the Black Lodge).
Now, we have also seen angels in the Red Room (remember the final FWWM scene?). I find it hard to believe that angels are Black Lodge residents. The Little Man From Another Place seems to inhabit the Red Room (he is always there as far as I know) but it is uncertain whether he is good or bad. He helps Dale Cooper to investigate through dreams but in FWWM he states: "I am the Arm!" which I take to mean "the arm that was cut off (by Mike/Philip Gerard)". This is further supported by the scene where the LMFAP puts his hand on Mike's stump and they speak in unison, telling BOB to give them their garmonbozia. LMFAP clearly eats the garmonbozia, indicating that he is evil, feeding off pain and suffering (I think it's Laura'a BTW, not Leland's).
Therefore, we have statements that the Red Room is in the Black Lodge, we have seen the Little Man who appears to be good and bad, and we have seen angels - all inhabiting the same place. We never see any hint of the Lodge containing more than this. Laura's spirit ends up in the Red Room also. Rather than a doorway to both worlds, the Red Room would seem to be both worlds.
I get the distinct feeling that both Lodges are the same, only differentiated by what one brings into the Lodge with onesself. Imperfect courage brings destruction. Fear opens the doorway to the evil side, while love brings in peace. The Lodge inhabitants all co-exist (as we see in the FWWM convenience store scene) with no apparent enmity between good guys (Tremonds/Chalfonts, for example) and bad guys (say, BOB).
To close this, I will remind any readers of the Giant's line in (I think) the final TP episode: "One and the same."
This concludes my thought for right now... More to come later.