From Likutei Ma-harich On Rising in the Morning

In the Gemara of Berachos, at the conclusion of Perek Haro-eh, we encounter the following: When he wakens he recites elokai neshama shenasata bi tehora...(My G-d, the soul that You have put in me is pure...). This is a blessing of thanks for G-d’s having returned to him his soul. However, it is not our custom to recite any beracha (blessing) before performing netilas yadayim – washing the hands. For the reason for our departure from the unqualified statement of the Gemara, see Rabeinu Yona’s comments to this passage in the Gemara, in which he explains that in the Talmudic era people were saturated with holiness. Consequently, they were punctilious about maintaining their sanctity, once having washed their hands. (In other words, they would wash their hands before retiring for the night and maintain their pure state throughout the night, by scrupulously refraining from touching themselves in places touching which would compromise their cleanliness.) We, on the other hand, who are incapable of steadily maintaining our cleanliness in a comparable manner, ought not to recite a blessing until having washed our hands. Consult this source for further details.

The Seder Olam states (and the Magein Avraham cites his statement at the conclusion of section 4) that one should offer praise and thanks to the Al-mighty, may His name be blessed, and enunciate immediately upon getting up [in the morning]: modeh ani lefanecha melech chai vekayam shehechezarta bi nishmasi bechemla raba emunasecha (I give thanks to You, the live, eternal Sovereign, for mercifully returning to me my soul. Immense is Your trustworthiness.) (One should pause briefly between the words bechemla and raba emunasecha. See the Yad Efrayim for more on this.) Reciting this does not require washing one’s hands, as neither a name nor an epithet is mentioned in this recitation-formula. See the Seder Olam for more on this. In regard to the intention behind the word bechemla, see what the Tola-as Yakov says in connection with the Elokai Neshama prayer, the gist of which is as follows. When the soul ascends at night On High to give an accounting of its actions, justice dictates that, if it should be found guilty, it should no longer be returned. See the Tola-as Yakov’s elaboration. The source of this assertion is the Zohar Hakadosh (Va-eschanan 269), where it said that, upon rising in the morning, the individual should offer praise to the Al-mighty for returning him his soul. It is an act of immense kindness on His part to have done so, considering that it is blemished with guilt in various ways and known to Him to be so. This notwithstanding, the Al-mighty restores his soul to his body. Consult this passage in the Zohar for further insight.

Now, the phrase raba emunasecha is to be understood in accord with the Midrash, cited by the Tur (46), which, citing the verse chadashim labekarim raba emunasecha, offers a simile: A man deposits one of his belongings to his friend for safekeeping, and this trustee returns it to him in a decrepit, ruined state. In contrast, when a man deposits his soul in a weary state to his Creator at night, He returns it to him in a renewed and much rejuvenated condition. This, then, is intimated by the phrase raba emunasecha (immense is Your trustworthiness). See the Midrash for further elaboration.