In the Bhagavad-gita the last instruction is to surrender fully unto Him the author of the Bhagavad-gita but unfortunate men of demonic mentality misunderstood the teachings of Bhagavad-gita as a method of sophistry and therefore the same Personality of Godhead Sri Krishna in the garb of a transcendental devotee preach the same techniques of Bhagavad-gita i.e. full surrender unto the almighty God or His different potencies in a demonstrative way.
The method of His demonstration was also very suitable. He inaugurated the sankirtana movement accompanied with melodious song which method has been found practically very effective amongst the masses. It is not possible for the masses to study the Vedanta or to undergo the difficult mystic processes especially in the Kali-yuga when the general people is indolent, unfortunate, shortlived and always disturbed by physical and mental tribulations.