As Vasishtha explains to Rama, the purest desires [=karma/action] gradually leads one to a state of lasting welfare in this world (life). And if one has trouble directing one’s destiny in such a way, one should exert the force of one’s activity to turn one’s mind to a profitable course.
First in chapter 2.7, Vasishtha motivates one to tune his own destiniy in this very life (world)
Having obtained a body free from disease and a mind free from trouble, one should try to know the knowable to prevent his further birth (in this world).
Whoso wishes to avert his destiny by means of his activity, obtains the acme of his wishes both in this world as well as in the next.
But whoever is averse to assiduity and relies in his luck, he is an enemy to his own soul, and sacrifices all his virtues, riches and hopes (to his idleness).
Then, in the following chapter, he already hints of the rectifying nature of good actions. This is the essence of the teaching. Basically, he says that on this very day, one is able to turn the course of one’s destiny previously plotted by one’s past karma.
What does destiny mean, which has no form, nor act, no motion nor might, but is a false notion rooted in the (minds) of the ignorant.
It is a word that has come into vogue from the idea of the future retribution of one's past actions [sva-karma-phala] (or retributive justice) and the like, which is designated "destiny".
From this the ignorant are led to believe that there is a thing as destiny: the inscrutability of which has led them to the fallacy as that of the supposition of a snake in a rope.
As a past misdeed of yesterday is rectified by a good action of the following day, let this day therefore supercede the past, and employ yourself to-day to action.
The perverted understanding that believes in a destiny grounded on its erroneous conception, may well enter into the fire from his conviction that it will not burn him unless it is so destined.
If destiny is the sole cause of every thing, why then should a man betake himself to his actions of bathing and making his offerings, sitting and walking, all of which may be done by his destiny.
Finally, in chapter 2.9. he reveals the imaginary nature of destiny which is the result of one's karma:
Destiny is a mere imaginary thing, which neither exists nor acts nor feels (their effects). It is neither seen nor regarded (by any body).
The good or bad result which proceeds from the accomplished acts of successful activity, is expressed by the word destiny.
The wished for and unwished for consequences resulting from the good and bad deeds of human activity, are termed the effects of destiny by people.
...
It is my belief and I have known it for certain that, destiny is no more than the word uttered by people upon their attainment of the object of their exertions [karma-phala].
This leads to a major lesson which teaches that destiny can be tuned to a state of lasting welfare by pure desires. Note how Vasishtha first says that Karma (action) and Vasana (Desire) are synonymous.
The mind is the soul and cause of all acts [karma] which they call the doings of destiny, certainly there is no other thing as destiny beside the mind.
This mind is verily the living soul, which acts as it desires, and enjoys accordingly the fruits thereof, and is same with destiny.
Know Rama that the mind, the heart, desire [vasana], action [karma] and destiny are synonymous terms, and applied by the virtuous to the unascertainable soul (evolved in these forms).
Now Rama admits he finds himself bound by actions of past lives. He asks Vasishtha: "Being caught in the net of my pre-existent desire, I remain a captive to them and do as they lead me to. Say then, O sage what else I can do."
Vasishtha continues the lesson on how to overcome one’s ‘destiny’ in this life:
So then O Rama, you will be able to reach to your lasting good, if you will but exert your activity for it, without which there is no other way to it.
These desires [vasana] are of two kinds, some leading to good and others to evil. Hence the desire of one's prior state must have been of one kind or other.
If you will be guided now by the pure desires [vasana] (of your nature), you will be gradually led by means of your good acts to attain the state of your lasting welfare.
But if your wrong inclinations tend to lead you to difficulties, you must try your best to overcome such propensities perforce.
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The current of our desires is flowing betwixt the two channels of good and evil; it must be by exertion of our activity that we must turn it to the right course.
You who are the mightiest of the mighty, must exert the force of your activity to turn your mind to a profitable course from its direction to the profitless.
