Krishna spoke the Bhagavad Gita - no argument there. Some 4500 years later, Krishna appeared as Lord Chaitanya to demonstrate how one should practice devotional service to Krishna. Once, in a conversation with His close associate Ramananda Raya, Lord Chaitanya reveals the ultimate purpose of human life.
Below is the Q&A between Chaitanya Mahaprabhu and Ramananda Raya.
Question by Lord Chaitanya: Please quote some verses from scripture about the ultimate goal of human life
Answer1 by Ramananda Raya: "By following one's qualities of work, every man can become perfect. By worship of the Lord, who is the source of all beings and who is all-pervading, a man can attain perfection through performing his own work." - BG 45-46
Reason for rejection by Lord Chaitanya: Lord Caitanya said that such a life is simply external, indicating that if a man has a material conception of life he cannot attain the highest perfection, even if he follows all the ritualistic regulations. Indirectly He asked Rāmānanda to describe something superior to such an external exhibition.
Answer2 by Ramananda Raya: It is better to give Kṛṣṇa the results of one's fruitive activities. He quoted "O son of Kuntī, whatever you do, whatever you eat, whatever you sacrifice, whatever you give away, and whatever austerity you undergo to achieve some goal, everything should be dedicated to My service." - BG 9.27.
Reason for rejection by Lord Chaitanya: A worker’s identification with material existence cannot be changed without proper guidance. Such fruitive activity will continue one’s material existence. A worker is simply instructed here to offer the results of his work to the Supreme Lord, but there is no information given to enable one to get out of the material entanglement.
Answer3 by Ramananda Raya: “Give up all kinds of religiousness and just surrender unto Me, the Supreme Personality of Godhead. I shall protect you from all sinful reactions, and you will have nothing to be aggrieved over.” - BG 18.66
Reason for rejection by Lord Chaitanya: Renunciation in itself is not sufficient. There must be positive engagement. Without positive engagement, the highest perfectional stage cannot be attained.
Answer4 by Ramananda Raya: “When by cultivation of knowledge a person realizes himself to be nondifferent from the Supreme Absolute Truth, he becomes joyful and is freed from all kinds of lamentation and material desires. At that time he perfects his Brahman realization by seeing everyone on the same spiritual level. Such Brahman realization can elevate one to the transcendental stage of devotional service.” - BG 18.54
Reason for rejection by Lord Chaitanya: Simply by renouncing material results in Brahman realization one does not realize the spiritual world and spiritual activities. Although there is no material contamination when one attains the stage of Brahman realization, in that stage one is still not perfectly pure because there is no positive engagement in spiritual activity. Because it is still on the mental plane, it is external.
Final answer by Ramananda Raya:“My dear Lord, one should give up monistic speculation and the cultivation of knowledge altogether. He should begin his spiritual life in devotional service by receiving information of Your activities from a realized devotee of the Lord. If one cultivates his spiritual life by adhering to these principles and keeping himself on the honest path in life, then although Your Lordship is never conquered, You become conquered by the devotee following such a process.” - SB 10.14.3
Reason for acceptance by Lord Chaitanya: In this age, because most people are fallen and because there is no time to elevate them by a gradual process, the best course, according to Lord Caitanya, is to let them remain in whatever condition they are in but to engage them in hearing of the activities of the Supreme Lord as those activities are explained in the Bhagavad-gītā and Śrīmad-Bhāgavatam. The transcendental messages of the scriptures should be heard from the lips of realized souls. In this way a person may continue to live in whatever condition he is in and still make spiritual progress. Thus one can surely advance and fully realize the Supreme Personality of Godhead (goal of human life).
Conclusion: There is a clear hierarchy from low to high - (1) discharging one’s duties in the varṇāśrama-dharma system (2) devotional service mixed with fruitive activity (3) renunciation (4) devotional service mixed with the culture of knowledge. All of the above has mixture on the material plane.
The final destiny for the soul, therefore according to Mahaprabhu Chaitanya, is to listen submissively from a pure devotee about Krishna and accordingly engage in favorable discharge of devotional service free from selfish motives.