"I am sending an angel before you to guard you on the way" Exodus 23.20
The Hebrew word frequently used for angel in the Tanach means "messenger" or "emissary". Using the divine name of Adonai Tzevaot, best expressed in translation as "Commander of the Hosts of Heaven" as a starting point, the angel is sent on a divine mission from the heavenly hosts to do God's bidding in the human world.
In Parashat Mishpatim the angel, who is unnamed, fulfils a dual purpose: to the Israelites it is a guide, but also a manifestation of God as it bears the divine name, and to the Canaanites it is the vanguard of terror, destruction and dispossession.
Angelology, though a part of rabbinic Judaism, is not that fully developed in the Hebrew Bible. The reason for this may principally be that anything of a semi-divine nature that was accorded powers otherwise ascribed to God was viewed as an encouragement towards idolatry and the worship of other deities; and this is probably why all the angels who interact with human beings in the Tanach have no existence independent of the divine.
By inter-testamental times, however, and certainly in the rabbinic period, angels were playing a variety of roles in literature and thought and the rabbis do not seem to have discouraged a belief in their existence, or in the concept of an angelic hierarchy with the archangels at the top.
Today, as more people fall into faith-less secularism, angels are once more in vogue: they appear in books, on greetings cards, indeed a Google search brings up 162,000,000 results, albeit that the first one is a certain theatrical costumiers! It is as if the diminishing of belief in God has inspired a folksy, pseudo-mystic-like belief in angels. The poet G.K. Chesterton wrote of angels: "angels can fly because they take themselves lightly!" I cannot help feeling that by and large so should we, and not allow such quaint relics of earlier times distract us from our primary goal, to engage in the search for a meaningful relationship with our God.