"If You Don't Have Incredible Patience And Humility"
Rabbi Micha Golshevsky commenting on Tapping Into Deveykus:
Rav Morgenstern's answer was that merely learning this limud brings to da'as as I wrote from the Magid. Learning this chochma with a desire to come close to Hashem has tremendous power to purify.
We live surrounded by physicality. The surest way to transcend this is with the highest medicine of deep Kabbala along with Chasidus and sifrei machshava (such as the Ramchal) which teach us how to approach and relate to these deep teachings.
I also included the Purim story which highlights thinking as much as one can in Torah and holiness. What you think about shows your spiritual level in a very telling way and often leads to action. All action start in thought on some level (explained at great length in seforim, Likutei Halachos included.)
Da'as is not merely theoretical. Da'as grows out of a deep connection to holiness which is strengthened by thinking about and enjoying Torah at least Niglos and preferably deeper Torah as well. Even learning these inyannim purify. The Rama (virtually) begins Shulchan Aruch: shivisi Hashem l'negdi samid. The Be'er Heitiv and Mishna Berurah, bring the Arizal who says that focus on Hashem's name brings yirah. Sounds quite practical to me.
Also let's not forget the word "samid". We are adjured to always be thinking about Hashem whether in learning or in desire to do a mitzva (such as the six mitzvos temidios brought in the first Biur Halacha, which are also done by thought.)
What you think is what you are.
I don't think there is anything theoretical about this.
I almost included the following in the post: "When I later saw the words of Rav Wolbe, zt"l, advising a young man how to cleave to Hashem at all times, I was reminded of that Purim. "First of all, this is a very high level to aspire to and takes much toil. This level entails always thinking about Torah concepts. But know that you must prepare many since it is difficult to think about the same idea for too long. If you think overly much about one concept, it will often become stale and uninspiring. You must have enough interesting questions or concepts prepared to take you through the entire day when you are not sitting over a sefer…"
It is just hard to do, in Niglah especially. In Nistar you just need a willingness as Rav Morgenstern said.
Of course, you are correct that Rabeinu gave Rav Nosson virtually the same advice regarding Kisvei Arizal, but I knew an extremely erudite Breslover who knew Shas and Poskim but couldn't get the Arizal.
He knew the sichah but didn't realize that unlike everything else in his experience (including Chasidus,) he will not see how even what he has understood, fits with anything else he knows and understands, period. No matter who he asks or how hard he is willing to work, he is back in cheder in terms of this chochma. This chochmah is designed to be incomprehensible until you have worked hard for a long time. Unlike Shas or Shulchan Aruch where you can ask and work and figure out what it means on the spot and how everything fits. But the Arizal is different. You will not be able to grasp the Arizal if you don't have incredible patience and humility. If you do learn this patiently with humility and a fiery yearning, there is no more pleasurable limud even while you don't yet understand. You connect with Hashem on a very personal level; could there be any more practical advice than that?