In plain words
that is to say, the beginning. There is no place at all for cowards in the spiritual field. The wicked, those without firm faith, doubters, and weeping-faced people are fit only to remain disciples to physicians — they can never become yogis. This precisely is the difference between the wise and the ignorant. 'As though laughing', Kṛṣṇa, overflowing with joy, spoke laughingly, while grief-stricken Arjuna listened; the wise always laugh, while the ignorant keep weeping.
For inquiry into the Ātma, the duty proper to one's stage of life is exceedingly necessary. Knowledge of that duty is something one must acquire for oneself. Until childhood passes, a person cannot become a dweller in any āśrama at all; until then, he has no special knowledge accruing to him whatsoever.
Just as the living body passes through childhood, boyhood, youth and old age, knowledge too has four corresponding states. In the first, childhood, one's life, being in the stage of ignorance, should accept discipleship — servitude and training — with no responsibilities at all, and continuously pursue the acquisition of knowledge. In the second stage, youth, one should undertake the responsibility of managing society, remain vigilant in earning wealth and in its use, provide fitting guidance and ideals to those younger than oneself, follow one's elders, and continuously gain in the growth of knowledge. In the third stage, maturity, one should bear the burden not merely of one's own community and family, but of the people's welfare and its administration, striving for the world's good without regard even for one's own comfort, and should continue acquiring inner Jñāna. In the fourth, old age, having grasped from one's own prior experience that worldly pleasures and the like are without substance and impermanent, one should become endowed with understanding, compassion and goodwill toward all beings, and proclaim one's own experiential knowledge to the world. Thus the qualities and functions of beings appear as four such classes.