One can understand how much he has advanced

This is also confirmed in Bhagavad-gītā (14.11-13):

sarva-dvāreṣu dehe 'smin

prakāśa upajāyate

jñānaḿ yadā tadā vidyād

vivṛddhaḿ sattvam ity uta

lobhaḥ pravṛttir ārambhaḥ

karmaṇām aśamaḥ spṛhā

rajasy etāni jāyante

vivṛddhe bharatarṣabha

aprakāśo 'pravṛttiś ca

pramādo moha eva ca

tamasy etāni jāyante

vivṛddhe kuru-nandana

"The manifestations of the modes of goodness can be experienced when all the gates of the body are illumined by knowledge.

"O chief of the Bhāratas, when there is an increase in the mode of passion, the symptoms of great attachment, uncontrollable desire, hankering, and intense endeavor develop.

"O son of Kuru, when there is an increase in the mode of ignorance, madness, illusion, inertia and darkness are manifested."

The Supreme Personality of Godhead, who is present in everyone's heart, simply gives the results of the increase in the various qualities, but He is impartial. He supervises victory and loss, but He does not take part in them.

The various modes of material nature do not work all at once. The interactions of these modes are exactly like seasonal changes. Sometimes there is an increment of rajo-guṇa, sometimes of tamo-guṇa and sometimes sattva-guṇa. Generally the demigods are surcharged with sattva-guṇa, and therefore when the demons and the demigods fight, the demigods are victorious because of the prominence of their sattva-guṇa qualities. However, this is not the partiality of the Supreme Lord.

By external features one cannot understand who is favored by Kṛṣṇa and who is not. According to one's attitude, Kṛṣṇa becomes one's direct adviser, or Kṛṣṇa becomes unknown. This is not Kṛṣṇa's partiality; it is His response to one's ability to understand Him. According to one's receptiveness — whether one be a devatā, asura, Yakṣa or Rākṣasa — Kṛṣṇa's quality is proportionately exhibited. This proportionate exhibition of Kṛṣṇa's power is misunderstood by less intelligent men to be Kṛṣṇa's partiality, but actually it is no such thing. Kṛṣṇa is equal to everyone, and according to one's ability to receive the favor of Kṛṣṇa, one advances in Kṛṣṇa consciousness. Śrīla Viśvanātha Cakravartī Ṭhākura gives a practical example in this connection. In the sky there are many luminaries. At night, even in darkness, the moon is extremely brilliant and can be directly perceived. The sun is also extremely brilliant. When covered by clouds, however, these luminaries are not distinctly visible. Similarly, the more one advances in sattva-guṇa, the more his brilliance is exhibited by devotional service, but the more one is covered by rajo-guṇa and tamo-guṇa, the less visible his brilliance, for he is covered by these qualities. The visibility of one's qualities does not depend on the partiality of the Supreme Personality of Godhead; it is due to various coverings in different proportions. Thus one can understand how far he has advanced in terms of sattva-guṇa and how much he is covered by rajo-guṇa and tamo-guṇa.