The punishment by fire in Leviticus 21:9 is a death sentence. There is no concept of purification by fire for people in the OT.
This law is stated in the context of a chapter that deals with priestly law, not with general law that applies to all of the tribes. Because Israelite society is stratified and hierarchical, there is no reason to assume that the laws specifically stated for one strata should apply to any other. In general, the hierarchy of the strata by holiness and by civil privilege is:
- The high priest
- Serving priests (with verified lineage)
- Non-serving priests, hallal priests and disfigured priests
- Levites who are not priests
- Members of the other eleven tribes
- Converts and freed Canaanite slaves (without tribal affiliation)
- Israelite slaves (eventually freed)
- Gibeonites (never to be freed, but provided territory of their own)
- Non-Israelites (except as noted below)
- Egyptian converts (allowed to marry Israelites at the third generation)
- Male Amonites and Moabites (not allowed to marry Israelites even after conversion)
- Canaanite slaves (never to be freed)
- Non-Israelite members of the seven nations of Canaan (to be exiled on sight)
- Amalekites (to be killed on sight)
So this is not an egalitarian model of society. Each strata has separate laws although portions of the law apply to all strata. In addition to these divisions, there are divisions within strata such as by gender and by age.
The translation that you have quoted is not sufficiently accurate to provide correct understanding of the verse.
The MT version of the verse is:
ובת איש כהן כי תחל לזנות את אביה היא מחללת באש תשרף
Which means (my translation):
And a daughter of a man who is a priest, when she begins to have relations out of wedlock, disqualifies her father, in fire she shall be burned.
The translation that you quote has the following inaccuracies:
- The word זנות, znoot, refers to relations out of wedlock between Israelites in the OT, not necessarily as a profession, so the OP translation "becoming a prostitute" is misleading. "Promiscuous" would be closer. There is no clear criteria for znoot in the OT, so there is a fundamental unclarity in how to apply this verse in practice.
- The word חלל, hallal, refers to a defilement, or when applied to priests, disqualification for the active priesthood. It is used in verses 4, 6 7, 12 14 15 and 23 as well as in verse 9 of this chapter with these two meanings, so the OP translation "disgraces her father" does not convey practical outcome of her actions for her father, disqualification from the active priesthood.
- The word תחל, tahel, has the meaning "when she starts". This has important ramifications for the validity of the priestly actions that her father might have performed after the start of her promiscuity but before he was officially disqualified. The OP translation completely misses this point by translating it as "becomes".
- The OP translation leaves out "the daughter of a man who is a priest" and collapses the translation to "a priests daughter". The seemingly extraneous inclusion of "a man" in the MT text opens the possibility of an interpretation that the penalty would only apply when her father is a man, that is, alive and can be disqualified, but that if he were deceased the penalty would not apply.
The OT is disdainful of promiscuity and relations out of wedlock, but there is no specific punishment. When done for financial gain (prostitution) there is even some indication of understanding that this is a last resort for marginalized women. The death penalty applies only for relations between a married woman and a man who is not her husband during her husband's lifetime. In this case, the death penalty is applied equally to the man and to the woman (Leviticus 20:10), though the case law is not symmetric in that there is no specified penalty for an unmarried woman who has relations out of wedlock with a married man.
The analysis in this post borrows from Dr. Nahum Avraham's well researched and scholarly reviewed monograph Marginal People in Time of the Bible, "Empty", "Impetuous", "Unclean", Homosexual, Prostitutes and Cult Prostitution published in Hebrew by the Bialik publishing house in their The Biblical Encyclopaedia Library series.