In the Śrīmad-Bhāgavatam, this is explained; vadanti tat tattva-vidas tattvaṁ yaj jñānam advayam. "Those who are actually knowers of the Absolute Truth know that the Self is realized in three different phases as Brahman, Paramātmā and Bhagavān." (SB 1.2.11) Bhagavān is the last word in the realization of the Absolute Truth; therefore one should reach up to that platform of understanding the Supreme Personality of Godhead and thus engage in the devotional service of the Lord. That is perfection of knowledge.
Beginning from practicing humility up to the point of realization of the Supreme Truth, the Absolute Personality of Godhead, this process is just like a staircase beginning from the ground floor up to the top floor. Now on this staircase there are so many people who have reached the first floor, the second or third floor, etc., but unless one reaches the top floor, which is the understanding of Kṛṣṇa, he is at a lower stage of knowledge. If anyone wants to compete with God and at the same time make advancement in spiritual knowledge, he will be frustrated. It is clearly stated that without humility understanding is harmful. To think oneself God is most puffed up. Although the living entity is always being kicked by the stringent laws of material nature, still he thinks, "I am God" because of ignorance. One should be humble and know that he is subordinate to the Supreme Lord. Due to rebellion against the Supreme Lord, one becomes subordinate to material nature. One must know and be convinced of this truth.