ananya bhakti is the way to moksha

Arjuna fails to get established in the divine vision. The primary reason is that he has still not realized the "vasudeva sarvam" even after the divine internal perception granted by the LORD. So, he requests LORD to appear in his normal human form. LORD grants his wish.
Arjuna then declares: (11.51)

O Janardana, having seen this serene human form of Yours-gracious, as of my friend I have now become calm in mind and restored to my own nature.

Having heard this LORD gives an important Instruction as follows:

Instruction 27:
श्री भगवानुवाच
सुदुर्दर्शमिदं रूपं दृष्टवानसि यन्मम।
देवा अप्यस्य रूपस्य नित्यं दर्शनकाङ्क्षिणः।।11.52।।
su-dur-darsam, idam rupam drustvaanasi yat mama
deva api yasya rupam nityam darsana-kaankshinah.

This "simultaneously brilliant and terrifying form" (su dur darsam idam rupam) that you have seen is desired to be seen even by the Devas (the shining ones - gods) always!

नाहं वेदैर्न तपसा न दानेन न चेज्यया।
शक्य एवंविधो द्रष्टुं दृष्टवानसि मां यथा।।11.53।।
na aham vedaih na tapasaa na daanena na ca ijyayaa
sakya evam vidhe drastum drustuvaan asi maam yathaa.

Not through the four Vedas, not by tapas (austerity like chandrayana etc.,) not by giving gifts like land, gold etc., not even by sacrifices and worship I can be seen in the form that has been seen by you.

भक्त्या त्वनन्यया शक्यमहमेवंविधोऽर्जुन।
ज्ञातुं दृष्टुं च तत्त्वेन प्रवेष्टुं च परंतप।।11.54।।
11.54 भक्त्या by devotion, तु indeed, अनन्यया single-minded, शक्यः (am) possible, अहम् I, एवंविधः of this form, अर्जुन O Arjuna, ज्ञातुम् to know, दृष्टुम् to see, च and, तत्त्वेन in reality, प्रवेष्टुम् to enter into, च and, परंतप O Parantapa (O scorcher of the foes).

But only through "bhaktyaa ananyayaa" (bhakti based on "no second thought") it is possible.

मत्कर्मकृन्मत्परमो मद्भक्तः सङ्गवर्जितः।
निर्वैरः सर्वभूतेषु यः स मामेति पाण्डव।।11.55।।
11.55 Pandava, O son of Pandu; yah, he who; mat-karma-krt, works for Me: work for Me is mat-karma; one who does it is mat-karma-krt-.Mat-paramah, who accepts Me as the supreme Goal: A servant does work for his master, but does not accept the master as his own supreme Goal to be attained after death; his one, however, who does work for Me, accepts Me alone as the supreme Goal. Thus he is matparamah-one to whom I am the supreme Goal-.So also he who is madbhaktah, devoted to me: He adores Me alone in all ways, with his whole being and full enthusiasm. Thus he is madbhaktah - Sanga-varjitah, who is devoid of attachment for wealth, sons, friends, wife and relatives, Sanga means fondness, love; devoid of them - Nirvairah, who is free from enmity; sarva-bhutesu, towards all beings-berefit of the idea of enmity even towards those engaged in doing unmost harm to him - Sah, he who is such a devotee of Mine; eti, attains; mam, Me. I alone am his supreme Goal; he does not attain any other goal. This is the advice for you, given by Me as desired by you.

This last verse of 11th Adhyaya is considered as the overall purport of Srimad Bhagavad Gita by Adi Sankaracharya.
Also,
Sri Abhinava Gupta on last two verses says as follows:
Those, whose devotion, charming by the absence of any other object in it, bursts forth-to the field of realisation of those persons descends the Vasudea - tattva, the Absolute being, without any effort (on their part) just on account of their appreciation of the advice given earlier as 'Having the realisation that Vasudeva is all, one takes refuge in Me. etc.'

om tat sat