The rishis of old attained the Knowledge of Brahman. One cannot have this so long as there is the slightest trace of worldliness. How hard the rishis laboured ! Early in the morning they would go away from the hermitage, and would spend the whole day in solitude, meditating on Brahman. At night they would return to the hermitage and eat a little fruit or roots. They kept their mind aloof from the objects of sight, hearing, touch, and other things of a worldly nature. Only thus did they realize Brahman as their own inner conciousness.
It is not lust alone that one should be afraid of in the life of the world. There is also anger. Anger arises when obstacles are placed in the way of desire.
Men are like pillow-cases. The colour of one may be red, that of another blue, and that of the third black; but all contain the same cotton within. So it is with man; one is beautiful, another is ugly, a third holy, and a fourth wicked; but the Divine Being dwells in them all.
You speak of doing good to the world. Is the world such a small thing? And who are you, pray, to do good to the world? First realise God, see Him by means of spiritual discipline. If He imparts power you can do good to others; otherwise not.