This discourse was taught by the Rebbe on Shabbat Sedra Kedoshim, in 1967.  The command 'you should be holy' (Leviticus 19:2) at the beginning of the Sedra is explained by Nachmanides to mean 'sanctify yourself in that which is permitted to you', which an extra level of personal stringency, beyond the basic demand of the Code of Law.  

The discourse discusses the nature of existence, how it can reveal the Essence of the Divine.  The path to achieve this perception is by fulfilling the Commands of the Torah and, in particular, making the extra step of sanctifying oneself in that which is permitted.