Bhagavad-Gita: Chapter 4, Verse 40

Rudra Vaisnava Sampradaya:

Visnuswami

Sridhara Swami's Commentary

After previously describing the qualifications of an aspirant for spiritual knowledge now Lord Krishna describes the characteristics of one who is unfit and not qualified for spiritual knowledge. One who is ignorant, of little faith, who does not follow instructions of the spiritual master, who doubts the teachings of the eternal Vedic scriptures. Such a person has no chance for spiritual awakening and their human birth was all for nothing and in vain. One who doubts is ruined in this life for one will have little or no success in this world and such a person will have nothing in the next life either because of not acquiring any merit in this life. Nor will there be any happiness for them as due to always doubting one is unable to enjoy anything and thus pleasure for them also is an impossibility.

Brahma Vaisnava Sampradaya:

Madhvacarya
There is no commentary for this verse.

Sri Vaisnava Sampradaya:

Ramanuja

Ramanuja's Commentary

The word ajnah means fool or one who is uninstructed in Vedic wisdom. The word asraddadhahanah means one who has no faith even after being instructed. The skeptic is one who doubts the knowledge one has already received. One of this disposition perishes for one who doubts the veracity of the atma or soul and the validity of the teaching taught by the spiritual master has no hope in this world or in the heavenly spheres. That is because sacrificing the three goals of human existence being dharma or righteousness, artha or wealth and kama or pleasure. What chance will one have for the fourth being moksa or liberation? For all the ambitions of humans are accomplished by performing some prescribed duty in the Vedic scriptures and fulfilment of any desire is dependent on the conviction that the atma or soul is eternal and the atma is distinct from the physical body. Whoever doubts the existence of the atma or soul or is not sure that it is eternal cannot receive even the smallest percentage of spiritual bliss.

Kumara Vaisnava Sampradaya:

Nimbaditya

Kesava Kasmiri's Commentary

After explaining concisely how the person of faith acquires spiritual knowledge through the instructions of the spiritual master, Lord Krishna speaks of the miserable fate of the ignorant who are devoid of faith but in this verse He uses the particle ca twice meaning again and again is given to indicate that by the mercy of the spiritual master even the ignorant if they have faith can be eventually liberated by performing some easy simple practice as determined by the spiritual master. But a person with no faith will not engage themselves in any practice because they do not believe. Still one with no faith may still have a chance to be liberated even without practising if they have some association with self realised beings or if they take the opportunity to render service to them. The doubting is of a more severe nature as doubting of the instructions of the spiritual master, doubting the authority of the Vedic scriptures, doubting the superiority of Vaisnavism, doubting the reality of the deities presence. All these things put ones mind in a hellish condition and with an unstable mind one does not follow any path fully but runs hither and thither and thus deviates from the natural path of human beings which is only found in the Vedic scriptures. For the doubter of little faith there is no happiness in this world or the next having performed no spiritual activities in this life such as even marriage which is a sacred rite and thus having no offspring from marriage which is also a sacred rite and thus by not accruing any spiritual merit in this life ones chance for happiness in the next life are bleak and grim as well. The meaning is how is it possible for such persons ever to become liberated if they doubt the very essence that they received their existence from.