The Vedanta Sutras of Badarayana, Commentary by Sankara (SBE38), tr. by George Thibaut  at sacred-texts.com
51. In this life also (the origination of knowledge takes place) if there is no obstruction of what is ready at hand; on account of this being seen (in scripture).
Beginning from Sûtra 26 of the present pâda we have discussed the various means of knowledge. We are now to consider whether knowledge--the fruit of those means--when accomplishing itself accomplishes itself only here in this life, or sometimes in the next life only,--The pûrvapakshin maintains that it accomplishes itself here in this life only. For, he argues, knowledge has for its antecedent the learning of scripture and so on, and nobody applies himself to learning, &c., with the intention that knowledge should result therefrom in the next life only; we rather observe that men begin to learn with a view to knowledge already springing up in this life. And also sacrifices and the like produce knowledge only mediately through learning and so on; for knowledge can be produced (directly) through the means of right knowledge only 1. Hence the origination of knowledge takes place in this life only.--To this we reply, 'The origination of knowledge takes place in this life if there is no obstruction of that which is ready at hand.' That means: When the means of knowledge which is operative is not obstructed by some other work the results of which are just then reaching maturity, knowledge already reaches maturity in this life.
[paragraph continues] But when such an obstruction takes place, then in the next life. And a work's reaching maturity depends on place, time, and operative cause presenting themselves. Nor is there any binding rule according to which the same time, place, and operative cause which ripen one work should ripen another work also; for there are works the fruits of which are opposed to each other. And scripture also goes only so far as to teach what the fruit of each work is,, without teaching the special conditions of place time, and operative cause. And owing to the specific strength of the means employed the supersensuous power of one, work manifests itself (i.e. the fruit of that work realizes itself), while that of another is obstructed thereby and comes to a standstill.
Nor is there any reason why a man should not form, with regard to knowledge, an unspecified intention 1; for we may freely form the intention that knowledge should spring up from us cither in this life or in some subsequent life. And knowledge although springing up through the mediation of learning and so on, springs up only in so far as learning destroys the obstacles in the way of knowledge. Thus scripture also declares the difficulty of knowing the Sell, 'He of whom many are not even able to hear, whom many even when they hear of him do not comprehend; wonderful is a man when found who is able to teach him; wonderful is he who comprehends him when taught by an able teacher' (Ka. Up. I, 2, 7).--Moreover scripture relates that Vâmadeva already became Brahman in his mother's womb, and thus shows that knowledge may spring up in a later form of existence through means procured in a former one; for a child in the womb cannot possibly procure such means in its present state.
The same is shown by Smriti. Vâsudeva being asked by Arguna, 'What will be the fate of him, O Krishna, who has not reached perfection?' replies, 'None who performs good works undergoes an evil fate;' declares thereupon
that such a man reaches the world of the blessed and is, later on, born again in a good family; and finally states just what we at present maintain in the passage beginning, 'There he obtains that knowledge which corresponds to his former bodily existence,' and closing, 'Perfected by many states of existence he then goes the highest way.'--It therefore is an established conclusion that knowledge originates, either in the present or in a future life, in dependence on the evanescence of obstacles.
327:1 Of which study is one.--Sacrifices indeed may bear their special fruits in the next life only; but in so far as they co-operate towards knowledge they are effective in this life. For their only action in that line is to purify the mind and thus to render it fitter to receive knowledge.
328:1 I.e. there is no reason for the assertion made by the pûrvapakshin that men form a specified intention only, viz. that knowledge should spring up in this life only.