Disciple Number One:

“My Gurudeva is the highest. He is a nitya siddha devotee who only descended for us.”

Disciple Number Two:

“My Gurudeva is the highest. He is a sadhana siddha devotee who attained perfection to save us.”

Shastra:

ācāryaṁ māṁ vijānīyān
nāvamānyeta karhicit
na martya buddhyāsūyeta s
arva devamayo guruḥ
(Śrīmad Bhāgavata 11.17.27)

“You should know the ācārya to be Me, never slight or disrespect him or find faults in him, considering him to be an ordinary mortal, for Śrī Gurudeva is the aggregate of all the Gods.”

yasya sākṣād bhagavati jñāna dīpa prade gurau
martyāsaddhiḥ śrutaṁ tasya sarvaṁ kuñjara śaucavat
(Śrīmad Bhāgavata 7.15.26)

“Whoever sees the Guru, the bestower of the lamp of divine knowledge, who is God Himself, as a mere mortal, has all his learning lost, just as an elephant throws dust all over himself after bathing.” 

Śrī Viśvanātha Cakravartīpāda comments on this verse – sākṣād bhagavatīti bhagavad aṁśa-buddhir api gurau na kāryeti bhāvaḥ. yad vā upāsye bhagavatyeva sākṣād vidyamāne martyā’sad dhīḥ martya iti durbuddhis tasya śrutaṁ bhagavan mantrādikaṁ śāstrādikaṁ śravaṇa mananādikaṁ ca vyartham ityarthaḥ

“Sākṣād Bhagavan means one should not even see the Guru as a particle of God, but as God Himself. It is foolish if one sees God, who is directly present (in the form of the Guru) as a mortal. If a fool thinks the Guru is an ordinary mortal not only his learning, but also his practise of his mantra, his hearing and his meditation on the Lord are all in vain.”

eṣa vai bhagavān sākṣāt pradhāna-puruṣeśvaraḥ yogeśvarair
vimṛgyāṅghrir loko yaṁ manyate naram
(Śrīmad Bhāgavata 7.15.27)  

“He whose lotus-feet are sought by the greatest masters of Yoga, who is the Lord of material nature and all living beings has appeared in the form of Gurudeva, whom the people mistake for an ordinary human being.”  

Why is Gurudeva mentioned in the translation and not in the verse? Because the ācāryas explain the verse as such. Śrīla Jīva Gosvāmī explains:

eṣa śrī-kṛṣṇa-lakṣaṇo’pi. tataḥ prākṛta-dṛṣṭir na bhagavat-tattva-grahaṇe pramāṇam iti bhāvaḥ – “This is also the symptom of Śrī Kṛṣṇa (so if it is not about Kṛṣṇa it is about Guru, who was discussed in the preceding 5 verses). It shows that a mundane view can never help establish the truth about God.” 

Śrīla Viśvanātha Cakravartī confirms this more elaborately in his own comment:

nanu guroḥ pitṛ putrādayaḥ prativeśinaś ca taṁ naram eva manyante katham eka evāyaṁ śiṣyas taṁ parameśvaraṁ manyante? ata āha – eṣa iti bhagavān yadunandano raghunandano vā vai niścitam eva pradhāna puruṣayor īśvaraḥ yaṁ lokas tad avatāra kālotpanno janaḥ naraṁ manyate tena kiṁ sa naro bhavati? api tu parameśvara evetyevaṁ guror apīti bhāvaḥ –  

“If his parents, children and neighbors consider the Guru to be a human being then how can one disciple consider him to be the supreme controller (parameśvara)? To this it is said: When the master of the material nature and the living beings descends as Yadunandana (Kṛṣṇa) or Raghunandana (Rāma) and people who meet Him while He is down here on earth, take Him to be a human being, does that mean that He is? He is certainly the supreme controller, and so is the Guru.” 

“The guru is the Lord’s kāruṇya ghana vigraha, the embodiment of His great mercy. Just as water becomes ice when it is exposed to severe coldness, the Lord also appears on earth, assuming the tangible form of the guru when His compassion becomes condensed.  

guru kṛṣṇa rūpa hon śāstrera pramāṇe
guru rūpe kṛṣṇa kṛpā korena bhaktagaṇe
(C.C.)  

“The Guru is another form of Kṛṣṇa, that is proven by the scriptures. Kṛṣṇa bestows His mercy upon the devotees in the form of the Guru.”

Through all this scriptural evidence, it can be known that Śrī Kṛṣṇa appears in this world in the form of the Guru to extend His grace upon the devotees. This grace consists of the treasure of worshipping Śrī Kṛṣṇa, and the fruit of this bhajana is the treasure of prema which is bestowed upon the surrendered disciple.  

yo’ntar bahis tanu-bhṛtām aśubhaṁ vidhunvann ācārya-caitya vapuṣā svagatiṁ vyanakti
(Bhāgavata 11.29.6)  

Śrī Uddhava told Śrī Kṛṣṇa — “O Lord! You remove all the people’s obstacles, in the form of sensual desires, to bhajana and grant them realisations about You, externally in the form of Śrī Guru, who is giving instructions in spiritual truths and internally in the form of the antaryāmī (the Inner Overseer) as good consciousness.”
(Srila Ananta das Babaji, Guru-Tattva-Vijnana)

DISCLAIMER:

“These quotes don´t apply to the siddha deha of Guru.”