Vaetchanan תרל”א 2

במדרש ואהבת את ה’ כו’ מי לי בשמים ועמך לא חפצתי כו’.
The Midrash on the pasuk of Shma Yisrael quotes the pasuk in Tehillim (73) who do I have in heaven and on the land I want nothing other than you. Just as in Shamayim I have no one else other than HaShem. So too in this world in spite of all the physical desires I wish for nothing other than HaShem. (this was the pasuk that Ba’al Hatanya lived with)
פי’ שלא להיות נמצא שום רצון אחר רק להש”י.
The meaning of this verse is that we should have no desire other than the desire for HaShem
נפשך בכל נפש ונפש שברא בך כו’.
The continuation of Shma is that one must love HaShem with all one’s nefesh. Meaning with every single desire.
ופי’ בכל לבבך אינו כמו עם כל לבבך כמו שמפרשין העולם.
And the explanation of the continuation of the pasuk ‘with all your heart’s this does not mean with your full.heart as many people explain
רק ממש בכל הרגשה שבאדם ידע שהוא רק חיותו מהש”י שאין אדם נוקף אצבעו כו’. והוא כגרזן ביד החוצב.
Rather that a person should feel that he is only in existence from HaShem and one cannot lift a finger without it having been declared from above. And one should be like the axe in the hand of the chopper. To completely nullify all of one’s desires to that of HaShem.
וזה ה’ אחד פי’ לבד שהוא אלקי אחד.
This is the meaning of HaShem is one. Besides for the simple meaning that there are no other gods
רק שהוא אחד אין עוד שכל דבר הוה הוא חיותו ית’ ממש
It also means that He is one and there is nothing else besides Him. Whatever there is in the world is His existence. It is a permeation of Him mamesh
רק שנסתר וכן רצונו ית’
However it is hidden. We do not see HaShem even though each thing is an actual part of Him. And this is essentially His will
א”כ צריך להיות נמצא אהבתו ית’ בכל הרגש שבאדם וזה בכל לבבך כנ”ל:
So therefore the love that we have for HaShem needs to be found in each and every feeling that a person has for it is all Him indeed. This is the (deeper) meaning of “…with all your heart”.