Zazen is about sitting without making distinctions. If a good feeling arises, we treat it the same as a bad feeling, we just let it arise and pass without judging it. Same for distinguishing between self and other, etc. Zazen is a practise for learning how to cultivate a mind that does not attach to discriminations or distinctions between different mental or physical states or objects.
We put distinctions on the world because we think it's necessary to be able to actually live here, but actually if you let go of distinctions you will find that life lives on as normal and you still somehow know what to do but in a much more liberated way.
"Not putting distinctions and discriminations on play" means to play without making distinctions or discriminations, such as: "am I playing right?", "am I being too loud?", "is this a good use of my time?", "could I be doing something more productive?", etc. Most adults cannot play without attaching to those questions and being bothered by them. One way to learn to not attach to those questions is to practise zazen