na karmanam anarambhan
naishkarmyam purusho ’snute
na ca sannyasanad eva
Not by merely abstaining from work can one achieve freedom from reaction, nor by renunciation alone can one attain perfection.
Commentary by Srila Prabhupada
The renounced order of life can be accepted when one has been purified by the discharge of the prescribed form of duties which are laid down just to purify the hearts of materialistic men. Without purification, one cannot attain success by abruptly adopting the fourth order of life (sannyasa). According to the empirical philosophers, simply by adopting sannyasa, or retiring from fruitive activities, one at once becomes as good as Narayana. But Lord Krishna does not approve this principle. Without purification of heart, sannyasa is simply a disturbance to the social order. On the other hand, if someone takes to the transcendental service of the Lord, even without discharging his prescribed duties, whatever he may be able to advance in the cause is accepted by the Lord (buddhi-yoga). Sv-alpam apy asya dharmasya trayate mahato bhayat. Even a slight performance of such a principle enables one to overcome great difficulties.
Commentary by Sri Visvanatha Cakravarti Thakur
This verse explains that without purity of heart, jnana does not take place. By not engaging in activities recommended in the scriptures, one cannot attain jnana (naiskarmyam). One with an impure heart cannot attain jnana by renunciation of activities recommended in the scriptures (sannyasat).