What is an Angel?

An angel is a spiritual being, and does not have any physical characteristics. The angelic descriptions provided by the prophets – such as wings, arms etc. – are anthropomorphic, referring to their spiritual abilities and tasks.

The Hebrew word for angel is "Malach," which means messenger; for the angels are G‑d's messengers to perform various missions.
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Some angels are created for one specific task, and upon the task's completion, cease to exist.

According to the Zohar, one of the angels' tasks, is to transport our words of prayer and Torah-study, before G‑d's throne.

Another type of angels are those, that are created through the deeds of man.
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In our daily prayers, we refer to the "songs of praise", which the angels sing before G‑d.

The angels have shifts, singing at designated times of day or night. The type of praise they sing, reflects the particular angel's spiritual status.

The angels' singing is alluded to in the story of Jacob's fight with the angel, at the end of which the angel pleaded with Jacob to free him "for the dawn has risen."
According to the Midrash, the angel's rush was because, his shift to sing before G‑d, had arrived.
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Seeing an angel, requires extra-sensory perception, as the bodies of the angels are not comprised, of all the basic elements of a physical being.
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Angels vs. Humans

Notwithstanding the great spiritual level of the angels, the holiness of the Jewish soul, supersedes that of the angel.

Only the Jewish soul has the ability, to descend to this physical and corporeal world, and refine and elevate it.

For the human's divine soul, is a "veritable piece of G‑d Above," a "piece" of the Creator; as opposed to the angels, which are only creations—albeit very holy ones.

This reflects itself in that fact that, angels are one-dimensional: each angels has one specific form of Divine service. The human soul, on the other hand, serves G‑d in many different ways, expressing itself through love, awe, etc.
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In the Tanya, Rabbi Schneur Zalman of Liadi writes,
that he heard from his masters, that "if one angel were to stand in the presence of a gathering of ten Jews, even if there were no words of Torah [being discussed] between them; such a boundless and infinite terror and dread would then befall him, (on account of the Divine Presence that abides over them), that he would become utterly nullified!"
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Furthermore, angels have no free-choice, and are pre-programmed to serve G‑d; whereas the human is entrusted with the mission of serving G‑d—but is given the freedom to choose, to do otherwise.