Immediately prior to detailing the forbidden sexual relationships, God declares: ‘My judgements you shall do and My decrees you shall safeguard; I am the Lord, your God’ (Lev. 18:4). The Torah’s use of two different terms – ‘judgements’ and ‘decrees’ – in the same sentence, seems strange. Rashi distinguishes between these two terms. He explains that the logic behind a judgement is clear. Decrees, on the other hand, are handed down by those with authority and are not necessarily always understood by those who are subjected to them. Thus, one generally understands the rationale behind judgements– for example, the prohibitions against murdering and stealing (Ex. 20:13) – and would observe them even without the existence of a command imposed by an external authority. In contrast, regarding decrees, such as the prohibition against wearing a garment that combines wool and linen (Lev. 19:19; Deut. 22:11), there would be no obvious reason to act in that way in the absence of an explicit command. Whilst the latter seems to lack the obvious reasoning of the former, they both derive from the same eternally binding divine source, and this is reinforced by the repetition of the aforementioned refrain: ‘I am the Lord, your God’ throughout this chapter that is entirely devoted to forbidden relationships (Lev. 18:2, 4-6, 21, 30). Why is the divine origin of these laws so strongly emphasised in this chapter?

If a liberal group of twenty-first century university students was asked to define a standard sexual ethic, their typical response would be expected to be that consenting adults may do whatever they want in private as long as it does not cause harm to or impede upon the rights of others. However, applying this principle to two consenting adult siblings would repulse many of these same students. Even though in principle, incest between consenting adults complies with the aforementioned standard, an intuitive morality forces most people to differentiate.

If moral laws are based on a subjective standard, eventually even the stipulation that the rights of others may not be impeded upon will be challenged. Hitler famously wrote:

Yes, we are barbarians! We want to be barbarians! It is an honourable title…Providence has ordained that I should be the greatest liberator of humanity. I am freeing men from the dirty and degrading self-mortifications of a false vision (a Jewish invention) called ‘conscience’ and ‘morality’ (Hermann Rauschning, Hitler Speaks).

When the standards of moral behaviour derive from a subjective source, the floodgates are thus opened. The Aztecs believed that human sacrifices were necessary for the sun to rise (Jacques Soustelle, Daily Life of the Aztecs), and the Torah mentions child sacrifice in the context of those worshipping the pagan deity Molech (Ramban on Lev. 18:21). These extreme historical precedents show the extent to which personal subjective ethics can justify acts that we today instinctively deem as immoral.

History shows the countless pitfalls of subjective morality. While not immune to tragic exceptions, Judaism has always revered an objective morality that adapts rather than changes in accordance with the context. Perhaps it is this philosophy that is the reason behind the Torah’s repetition of the phrase ‘I am the Lord, your God’ throughout the chapter dealing with forbidden relationships. In an ever-changing ethical landscape, the Torah serves as the objective moral compass for every individual, requiring us to be sensitive to others, while maintaining a constant sense of moral integrity.