I looked up sacred and found this definition: dedicated to a religious purpose. Religion is defined as
a set of beliefs concerning the cause, nature, and purpose of the universe, especially when considered as the creation of a superhuman agency or agencies, usually involving devotional and ritual observances, and often containing a moral code governing the conduct of human affairs (BBC, 2014).
In other words, the sacred is set apart from secular (or profane) life through belief in a deity or deities and the worship of those deities. How it is experienced differs from person to person, but there is this sense of specialness, this celebration of mystery, that is held separate from ordinary life.
In these days of “spiritual but not religious”, the definition seems to discount the experience of countless people finding deep, transcendent meaning to their lives and experiences without benefit of organized religion and church services. Some people find experiences in nature as sacred, set apart from the mundane moments of their life. Some find their volunteer work as sacred. Panentheists find the sacred permeating all of their life and do not see a separation of sacred and secular.
Apparently, we need to have the sacred in our lives, a glimpse into the infathomable, the Great Mystery.
BBC (2014). Religions. Available: http://www.bbc.co.uk/religion/religions/ [April 3, 2019].