The power of penance is impossible to defeat.

यदुष्करं यद्दुरापं यद्दुर्ग यच्च दुस्तरम् । 

तत्सर्वं तपसा प्राप्यं तपो हि दुरतिक्रमम् ॥'

 yaduṣkaraṃ yaddurāpaṃ yaddurga yacca dustaram । 

tatsarvaṃ tapasā prāpyaṃ tapo hi duratikramam ॥'

Parvathi the daughter of Himavan wants to woo the Lord Shankara as her life partner. After the Daksha episode and the self immolation of Sati, the Lord has become introvert and completely averse to worldly life and even the machinations of the Lord of Love Kamadeva could not make any dents into the steely determination towards celibacy on the part of the Supreme Lord.

It is in this backdrop that Parvathi is making her plans to gain a place in the heart of the Lord.

This situation is described in canto 5 of Kumarasambhavam of Kalidasa.

Penance, hard, dedicated, concerted penance alone would ensure for her success in her Mission. Here the quote from Manusmriti 11-238 is given by the commentator.

Whatever task that is impossible to perform, whatever destination that is impossible to reach, whatever place which is difficult to enter and pass through, whatever hurdle that is difficult to overcome, all that can be tackled by deep penance. The power of penance is impossible to defeat.

यद् दुष्करं अस्ति what is extremely difficult to do यद् दुरापं अस्ति what destination is difficult to attain यद् दुर्गं अस्ति which place is difficult to reach or negotiate यद् दुस्तरं अस्ति which hurdle is difficult to overcome तत् सर्वं all that तपसा साध्यं भवति can be tackled by penance तपः दुरतिक्रममं हि the power of penance is impossible to defeat.