Eved Ivri Perek 1, Class 6.
Lecture: the idea of Birur has two approaches, each with a different problem:
1) Birur from outside. you remain clean but you miss sparks.
2) Birur by Hislabshus, investment. You miss nothing but you get dirty.
The perfect Birur is בחכמה אתברירו when Chochma is mivarer (without any Hislabshus, but directly) it remains clean as it is disengaged, but the Gevura of פנימיות אבא פנימיות עתיק misses nothing.
Our Ma’amar describes the Birur of Da’as in a similar fashion.
It discerns what is important from what is unimportant without trial and error, just from depth.
Eved Ivri Perek 1, Class 7.
Inside, how Da’as clarifies priority absolutely and what is unholy is just not worthwhile.
It therefore automatically includes Gevura and Rachamim with it’s Chessed to have the proper judgement.
Thus the שין in עש”ב.