The Lord's Causeless Mercy Gives One the Ability to Render Service - Part 1

Dhruva Maharaja patiently executed his spiritual master Narada Muni's instruction, by doing so he attained the Supreme Perfection of life which was to receive darshan of the Lord. When the Lord was standing before him, he was speechless and stunned. He was unable to offer prayers in glorification of the Lord. The Lord very mercifully blessed him by touching His conchshell on his head.

He was thus enabled by the causeless mercy of the Lord , to offer fitting prayers.

• The Lord's mercy is needed to render service:
• Srila Prabhupada states in the purport to the verse 4.9.5:"To glorify or offer prayers unto the Supreme, one needs the Lord’s mercy. One cannot write to glorify the Lord unless one is endowed with His causeless mercy."
• Dhruva Maharaja experiences difference in himself:
• Therefore when Dhruva Mahārāja found this difference within himself, he could immediately understand that it was because of the causeless mercy of the Lord. 
• Acknowledgement and Gratitude for the mercy received
• He offered obeisances to the Lord with great respect and reverence, completely understanding that the Lord’s favor was upon him. 

How does such spiritual enlivenment work?

From Srila Prabhupada's purport to SB 4.9.6

• Action of the internal potency
• This spiritual enlivenment of Dhruva Mahārāja’s senses and mind was due to the action of the internal potency of the Lord.
• Connect with internal potency through chanting:
• Spiritual enlightenment is possible by the mercy of the spiritual energy of the Lord. The chanting of the Hare Kṛṣṇa mantra is first addressed to the spiritual energy of the Lord, Hare.
• When does the spiritual energy act:
•  This spiritual energy acts when a living entity fully surrenders and accepts his position as an eternal servitor. 
• When a person places himself at the disposal or order of the Supreme Lord, that is called sevonmukha; at that time the spiritual energy gradually reveals the Lord to him.
• Nothing is possible without the revelation by the spiritual energy
• Without revelation by the spiritual energy, one is unable to offer prayers glorifying the Lord.
•  Any amount of philosophical speculation or poetic expression by mundane persons is still considered to be the action and reaction of the material energy. 
• Action  of the spiritual energy:
• When one is actually enlivened by the spiritual energy, all his senses become purified, and he engages only in the service of the Lord. At that time his hands, legs, ears, tongue, mind, genitals — everything — engage in the service of the Lord. 
• Such an enlightened devotee no longer has any material activities, nor has he any interest in being materially engaged. This process of purifying the senses and engaging them in the service of the Lord is known as bhakti, or devotional service.
• "Mechanically Engaged" followed by "Engagement with spiritual understanding":
•  In the beginning, the senses are engaged by the direction of the spiritual master and śāstra, and after realization, when the same senses are purified, the engagement continues.
•  The difference is that in the beginning the senses are engaged in a mechanical way, but after realization they are engaged in spiritual understanding.

Further continued in 

The Lord's Causeless Mercy Gives One the Ability to Render Service - Part 2