Krishna of Srimad Bhagavatam and Krishna of Bhagavad-gita

What's the difference between Krishna of Bhagavad-Gita and Krishna of Bhagavatam?

In "Sri Guru and His Grace" Srila Guru Maharaja said: ”The substance should always be given a higher value than the form. First understand the degree of purity in Kṛiṣhṇa consciousness. The followers of form are only imitationists; they want only to exploit Mahāprabhu and not to serve Him." What does „degree of purity in Krishna consciousness” mean?