Source for Chasidik practice of imagining yourself giving up your life during the first verse of Krias Shma

Question

in a chassidus shiur i heard that the obligation for krias shma (for people busy with parnoso) according to all opinions is the first posuk of shma with kavono

and that the kavono is by saying it you are excepting the yoke of the kinship of haven (i guess the source of this is the mishna)
and that you are ready to give your live for echod (Hashem)
what is the source of this?

i thought that bicol nafshicha means this but what does it have to do the first verse and with the word "ehod"?

Answer 1

The first source is multiple, a mishna, a berayta with Rabbi Akiva, Rishonim.

1. Mishna Berachoth 9, 5 (pasted here from the Gemara with Soncino's translation)"

   'WITH ALL THY SOUL' MEANS, EVEN THOUGH HE TAKES THY SOUL [LIFE]"

   but the verse cited is the second verse and not the first.
2. Gemara Berachoth 61B

   When R`Akiba was taken. He prolonged the word ehad until he expired while saying it. A bath kol went forth and proclaimed: Happy art thou, Akiba, that thy soul has departed with the word "ehad"! see here

   It seems this is the first verse that is in question.
   The explanation is that Rabbi Akiva was amazed by the verse. He wondered, how is it possible to love G_d even when they kill us; that is to say, when it ceases to manifest his presence by the protection it has on us. The lack of perception of G_d is a sign that we are facing something far greater than previously believed. This means that we discover our blindness across as what it really is, and it is much more than what we were we represented (This is an idea often found in the books of Chassiduth, for example Rabbi Menachem Mendel Mivitebsk in Pri Ets, Drush Leparshath Teshuva If you understand this you may link what he says with this Gemara and an other Gemara with Rabbi Akiva that treat about midath hadin.). One day Rabbi Akiva was able to do all the effort he has developed this Cavana out of the Kriath Shema and in the general rapport with the existence of G_d. He is Echad, in all situations. It is in this spirit that we see a hint in several books as it has in the Rosh's Orchoth Chayim in Rishonim.
3. Here is Orchoth Chayim from HaRosh (his source is Igeret Hateshuva from Rabenu Yona). He extends this thought to the love of God in general. not just krias shema:

   לאהוב את ה' אלהיך בכל לבבך וגו', למסור גופך וממונך על קדושתו, ובזה תקיים בעצמך דברי המשורר "כי עליך הורגנו כל היום". לבטוח בה' בכל לבבך, ולהאמין בהשגחתו הפרטית, ובזה תקיים בלבבך הייחוד השלם בהאמין בו, כי עיניו משוטטות בכל הארץ, ועיניו על כל דרכי איש, ובוחן לב וחוקר כליות. כי מי שאינו מאמין "אשר הוצאתיך מארץ מצרים", אף ב"אנכי ה' אלוהיך" אינו מאמין, ואין זה ייחוד שלם. כי זה היה סגולת ישראל על הגויים, וזה יסוד כל התורה כולה:

4. Noam Elimelech, Tsetel Koton in the 2 first paragraphs developp the general idea and the cavana in KS. . The first is a general consideration, the second on krias shema. Here is it in wikitext.

I hope this may help you in this wonderful question.

And there is an English translation of the Tsetel Koton:

Answer 2

In short it is to fullfill the commandment to love Hashem with all your soul

See the second source of the excellent answer above

Brings that Rabbi Akiva explains that to love Hashem

"With all thy soul" means even if He takes away thy soul.

That the gemoro bings an example of this by going against the law to keep Hashem's commandments/will (when you love someone you want to be close to them and by doing their will you become close) and continues that

"When R`Akiba was taken out for execution, it was the hour for the recital of the Shema', and while they combed his flesh with iron combs, he was accepting upon himself the kingship of heaven.

We know from the mishna that the recital of the first chapter of shma is the accepting of the kingship of heaven.

So from this it seems the love of Hashem is even more revealed by fulfilling the spesific commandment/will of saying the shma (3 chapters) and spesificly the accepting of the kingship of heaven

chaddidus seems to me to be mostly about love and fear of Hashem.
To love of Hashem (doing his will) is required even when Hashem is killing you ("even if He takes away thy soul.")
So by all mitzvot by having in mind (potential self sacrifice) that you will do His will even if He takes your life

But spesificly the mitzva of saying the shma (on the right time) and accepting of the kingship of heaven to all the heavens and the 4 directions of the earth (berachot 13b) by having in mind that you are ready to do this even when Hashem is killing you (as Rabbi Akiva did), you are filling the mitzva of loving Hashem to the fullest and biggest extent (possible in your situation (when your live is not being threatened))