Satguru is a visible manifestation of Akal Purkh, Nirankar (Formless God). Love with Satguru is the same as with formless God. It is out of Mercy and Compassion for His creation that the Lord embodies forth in the Luminous form of Satguru.
Sri Guru Nanak Sahib is the Holy Image of God. A saint whose mind and physical eyes have been spiritualized, have been divinized by constantly drinking the Nectar of beholding this Holy Image cannot live without this life-breath even for few moments. The blessed one who has realized and tasted the Bliss of the Divine Glory of the Holiest of the Holy Image of Sri Guru Nanak Sahib cannot live without drinking this Nectar through his blessed eyes deep into his heart. Consequently his eyes sparkle and shine in this Divine Splendour, in the glory of Marvelleous Paramjot.