The 'Holiness Code' is the name Jewish scholars gave to the chapters 17 to 26 of the book Leviticus. The word 'Holy' had at that time an additional meaning to how we would use it today. Holy meant 'set apart' and especially to be set apart from their neighbors, both in behavior and worship. Whilst the tribes, that later would become Israel, worshiped only one God, its neighbors were polytheistic, worshiping many deities. And some of them even included Shrine (Temple) or Sacred Prostitution into their worship, see Deuteronomy 23:17 "No Israelite man or woman is to become a shrine prostitute."
The other need for these type of holiness stemmed also from the need of preserving one distinctive cultural identity as 'The Chosen People of God' amongst the many and varied neighboring tribes. So, the Holiness Code, at that time, helped people to:
- Be ritually clean in order to be able worship God in the right way.
- Be different from their neighbors in order to preserve their cultural identity.
- Be healthy by following dietary laws important for that time and climate.
- And, with regard to Leviticus 18:22, to procreate and increase in numbers.
Regarding the last point, it is important to note that at that time people believed that procreation was achieved when a man 'planted his seed' in the womb of a woman, the role of the woman was merely that of 'incubator' for his seed. This might explain why most Bible verses concerning homosexual acts were only concerned about those between two men, and not about those between two women. Procreation was incredibly important at that time as the Jewish tribes were outnumbered by powerful neighbors and one way to overcome this disadvantage was to grow the tribe. And the union of two men, or of two women, wouldn't have had any offspring.
Jews followed the Holiness Code until the year 70 of our time completely, but with the destruction of the temple in Jerusalem by the Romans, their main sanctuary, many of its laws and commandments regarding temple worship and sacrifice couldn't be followed anymore. Most Jews today will indeed still follow the dietary laws and all the others that don't relate directly to temple and sacrifice. Some Christians will make a kind of 'pick and choose' decision and will follow only a handful of these laws and commandments, normally ignoring all the dietary laws, but insisting that all the rules for sexual behavior laid out in the Holiness Code have to be followed.
On the other hand there are small groups of Christians that do follow the Jewish dietary laws still today and some Churches that don't teach that Homosexuality is a sin, but instead see it as a normal variation of human sexuality and even bless same-sex couples. The best known example for this is perhaps the Episcopal Church in America which ordained the first openly gay and partnered bishop in modern history, +Gene Robinson, Diocese of New Hampshire.
So, what is right? Whose interpretation is the correct one? What decides which laws we should still follow and which not? For this we have to delve deeper into the text.