To understand this better: The whole year we say in Krias Shema, (Devarim 11:15) “And I (Hashem) will give grass in your fields for your animals.” The deeper meaning of “your animals” is a reference to the animal soul and the human intellect (which is invested in the animal soul).
In order for them to agree to love Hashem (as mentioned in the Shema), the Sages established the blessing of Yotzer Or as the first of two blessings before the Shema, “והאופנים יחו...,” which describes how the angels, the Ofanim and Chayos, which are the spiritual source of the animal soul and the human intellect, have a great love for Hashem. Therefore, the animal soul and human intellect are also able to have a great love for Hashem, and they also established the Pesukei Dezimra (verses of praise of Hashem that the animal soul and human intellect can relate to on their own level).
The purpose of these is that through them, a person will come to a lengthy contemplation on the greatness of Hashem, to the point that even the animal soul and human intellect agree that it is proper for all living things, including myself, to yearn only for Hashem and nothing else.
However, to awaken the G-dly soul itself to love Hashem, this lengthy contemplation is not needed as much, since, as is says in Mishlei, (20:27) “The soul of man is a flame of Hashem.” Meaning that just like a flame is naturally drawn upwards to its source, so too it is the nature of the soul of every Jew that is derived from its source in Hashem, that its desire and yearning is to become absorbed in the Light of Hashem and to connect to Him. Since this love is inherent in every Jew's nature, therefore, not as contemplation is needed to awaken the love.
And this is the deeper meaning of what we say in the Shema, “And I (Hashem) will give grass in your fields for your animals.” The explanation: “Grass” is a reference to angels, who deliver the flow of life-force from Hashem to the lower created beings. Through them, Hashem’s flow of life-force is drawn down from Above to give power and strength to the G-dly soul, so that it should be able to transform the animal soul. Just like grass gives physical life to physical animals, so too the angels are sent to give spiritual life to the animal soul of man, by giving the person the ability to come to an understanding about Hashem and awaken a love for Hashem in his animal soul.
This “spiritual grass” to spiritually feed our animal soul with an understanding and love for Hashem is also derived from the 13 Attributes of Mercy that we mention throughout the year (as specified in Parshas Ki Sisa). During most of the year, we see Hashem's mercies expressed to us in two ways: To protect us physically and give us physical life. To enable us to refine and transform the animal soul that it should also come to love Hashem. However, in Elul, a different level of Hashem's mercies is expressed: This level of mercy from Hashem is specifically expressed in the rest of the year. However, regarding the month of Elul, it is written, “He nourishes us with roses,” which have 13 petals that correspond to the aspect of the “13 Attributes of Mercy” (as specified in Micha), that shine and are revealed in the month of Elul, which enable us to do Teshuva so that whatever revelation of Hashem was lacking due to our errors, should be filled in.
[Note of the Tzemach Tzedek: This drawing down of “roses” - corresponding to Hashem's mercies - are also needed for the G-dly soul itself. For, even though it is the nature of every Jewish soul to yearn to reconnect to Hashem, this does not explain why an extra power is needed for the G-dly soul to do Teshuva. The idea is that there is one level of the person’s own initiative to elevate himself to Hashem that comes from his own essential nature. But in order to reach the level of Teshuva that is “with greater strength,” beyond what the soul can do on its own, this drawing down from Above is necessary.]
