Before we go eons and eons back, let us first know what is ‘Ardhnarishwar’!
Splitting up we get Ardha – half, Nari – woman, Ishwar – Lord which is the Lord who has the feminine form in half of his body. Though there are many parallel tales behind this concept but what stands true is Lord Shiva in his androgynous form with Mother Parvati shares half of his body in the left side.
A Sanskrit verse composed in praise of Lord Shiva and Parvati heralds this concept of Shiva and Parvati being the Parents of this Universe.
वागर्थाविव संपृक्तौ वागर्थप्रतिपत्तये।
जगतः पितरौ वन्दे पार्वतीपरमेश्वरौ॥ १-१
vāgarthāviva saṁpṛktau vāgarthapratipattaye |
jagataḥ pitarau vande pārvatīparameśvarau || 1-1
As the word and its meaning are inseparable, The parents of the universe Parvati and Parameshwara exist as a two-in-one entity and I bow down to them in reverence.