Angels are, in a certain sense, spiritual animals. The prophet Ezekiel saw them with the face of a lion, the face of an ox (Ezekiel 1:10). The Tanya takes this literally: angels have no free will. Their love and fear of God are instinctive, hardwired into their nature, the way a lion is fierce and an ox is strong.
Rabbi Schneur Zalman of Liadi explains that this is precisely why righteous human beings outrank the angels. The souls of the tzaddik (a righteous person)im (צדיקים) dwell in the world of Beriah (בריאה), the world of Creation, while ordinary angels inhabit the lower world of Yetzirah (יצירה), the world of Formation.
The difference comes down to what drives them. In Yetzirah, only the emotional attributes (middot) of the Ein Sof (אין סוף) shine forth. Love and fear. That is all the angels get. The camp of the archangel Michael serves with love. The camp of the archangel Gabriel serves with awe. Day and night, without rest, they burn with these emotions. But they never chose to burn. They simply do.
In the world of Beriah, something higher shines: Chochmah, Binah, and Daat (חכמה, בינה, דעת), the intellectual faculties of the Infinite. Wisdom, Understanding, and Knowledge. These are the root and source of the emotions, and this is where righteous souls go, because their love and awe of God flow from genuine comprehension of His greatness.
When a human being prays with intention, meditating on the vastness of the Infinite until love or awe ignites in the heart, that prayer elevates not only the divine soul but the animal soul as well. The body itself becomes a vehicle for something the angels can never achieve: love that was earned, not given.