Here are my notes on some early Koresh letters at Mark Swett's site.
The following are writings from David's early years, when he still went by the name Vernon Howell. They were transcribed by defector Marc Breault. Note that Marc Breault was a dedicated opponent of David Koresh, so his selection of which writings to transcribe may have been influenced by a desire to make him look bad.
Also, some may be wondering why these letters are signed "VWH Jezreel." Jezreel was a prophetic title taken by Davidian leaders; the Davidian founder, Victor Tasho Houteff, signed some tracts "VH Jezreel." I suspect that David, then still known as Vernon Howell, may have signed these letters with his middle initial to avoid confusion with Houteff.
The links below go to Mark Swett's website:
Daughters Of Zion (Actually, this doesn't say who transcribed it, but Marc Breault is credited with transcribing all of the other letters in this section.)
Get Ready! (David closes this message by strongly urging Branch Davidians to come to the 1986 Passover. Some background: he had recently taken his second wife, and had finally convinced the Texas community to accept polygamy. However, most Branches were living on the outside, keeping in touch through study tapes, letters, visits from David Koresh, and trips to Texas, especially for Passover. David knew that if they were informed about his new teaching by tape, they would not accept it; this had to be sold in person. Thus, he wanted to make sure that all Branch Davidians would attend the 1986 Passover, where he could unveil his polygamy teaching.
This also relates to the letter's exhortations to study. One of his tactics was to tell Branches that the new light he would reveal was so mind-blowing that only the most spiritually advanced could accept it. He hammered home on the theme that they needed to study so that they would be spiritually prepared. After telling members at Passover about his second wife, there were those who retained private doubts, but they didn't want to admit out loud that they weren't spiritually advanced enough for this doctrine.)
Letter To Sister Smith (More urgings to come to the 1986 Passover.)
Letter To The Seventh-Day-Adventist Church
Blow Ye The Trumpet In Zion