CC Madhya 15.135
bhāgīrathī hana sākṣāt ‘jala-brahma’-sama
“Lord Jagannātha is the Supreme Lord Himself in the form of wood, and the river Ganges is the Supreme Lord Himself in the form of water.
The Vedas enjoin, sarvaṁ khalv idaṁ brahma: everything is the energy of the Supreme Personality of Godhead, the Supreme Brahman or Parambrahma. Parasya brahmaṇaḥ śaktis tathedam akhilaṁ jagat: everything is a manifestation of the energy of the Supreme Brahman. Since the energy and energetic are identical, actually everything is Kṛṣṇa, Parambrahma. In the Bhagavad-gītā (9.4) Lord Kṛṣṇa confirms this:
mat-sthāni sarva-bhūtāni na cāhaṁ teṣv avasthitaḥ
“By Me, in My unmanifested form, this entire universe is pervaded. All beings are in Me, but I am not in them.”
Kṛṣṇa is spread throughout the whole universe in His impersonal form. Since everything is a manifestation of the Lord’s energy, the Lord can manifest Himself through any energy. In this age, the Lord is manifest through wood as Lord Jagannātha, and He is manifest through water as the river Ganges. Therefore Śrī Caitanya Mahāprabhu ordered the two brothers — Sārvabhauma Bhaṭṭācārya and Vidyā-vācaspati — to worship Lord Jagannātha and the river Ganges.