Recall what the God of Death (Yama) told Nachiketas: ‘By means of impermanent entities we should reach the Permanent One’ (Kathopanishad: II – 10).
The true Sadhaka on the JnAna path would have already escaped from the sensual pleasures that are nothing but obstacles to spiritual growth and from those others which are far away from the Atman, like the pleasures of gossip, and of being an idler doing nothing.
But ordinary people like us (note that Periva includes Himself while talking about us mere mortals) who have to start from these beginnings, have to use our discretion (vivekaM) that can distinguish between the Permanent and the impermanent.
Movies, gluttony, addiction to coffee or cricket commentary, reading senseless fiction, excited gossip about politics – thus there are many more that attract us very forcefully. We have to be alert and keep thinking: ‘Would these things contribute even an iota to my spiritual growth? Should I give them so much importance?’ What can lead us to That Permanent One and what cannot? – a mercilessly strict balancing analysis is what nityAnityavastu-vivekaM means.
I said ‘mercilessly strict’ because our mind always tries to rationalize doing what it likes to do; it will find all sorts of justifications. Use the discriminatory power that does not give in to that kind of imagination and that judges this analysis very strictly, to assess ourself. See that it does not allow itself to ‘pass’ what deserves a ‘fail’.