וְנִשְׁמַרְתֶּם מְאֹד, לְנַפְשֹׁתֵיכֶם: כִּי לֹא רְאִיתֶם, כָּל-תְּמוּנָה, בְּיוֹם דִּבֶּר יְהוָה אֲלֵיכֶם בְּחֹרֵב, מִתּוֹךְ הָאֵשׁ
"[H]ere it is a matter of not allowing ourselves to be robbed of the clarity of our conception and the certainty of our conviction of the supernatural, invisible yet absolutely real and personal existence of God, by any intrusion of any idea of substantiality...
"Besides God, there is only one other being of whose individual reality and personal existence, although invisible and unable to be realised by any of our physical senses, each one of us bears within himself the direct certainty of conviction, and that is our soul, our Nefesh. It is that, therefore, which reflecting back on oneself makes one comprehend the real existence of something which is invisible and intangible, and by the certainty of the conviction of ones's own self comprehend the conviction of the existence of God. Therefore, "it is our soul that we lift up to God, therefore does our soul long for, thirsteth, languisheth for God...Therefore, "doth our soul seek God in the night...therefore "doth our soul cling to folliwng God...[and] therefore do our souls bless God.
"וְנִשְׁמַרְתֶּם מְאֹד, לְנַפְשֹׁתֵיכֶם accordingly in this connection means: Guard yourselves, keep, above all, the influence the knowledge of your soul exercises, for it comprehends that what cannot be grasped by your senses has a more real existence than what can be grasped by your senses so that God may remain for your, just in His insubstantiality the most real actual existing Being."
- Rav Hirsch on Devarim 4:15