In the Bible, angels are a medium of God's power; they exist to execute God's will. Angels reveal themselves to individuals as well as to the whole nation, to announce events, either good or bad, affecting humans. Angels foretold to Abraham the birth of Isaac, to Manoah the birth of Samson, and to Abraham the destruction of Sodom.
Guardian angels were mentioned, but not, as was later the case, as guardian spirits of individuals and nations. God sent an angel to protect the Hebrew people after their exodus from Egypt, to lead them to the Promised Land, and to destroy the hostile tribes in their way (Ex. 23.20, Num. 20.16).
They constitute God's court, sitting in council with Him (I Kings, xxii. 19; Job, i. 6, ii. 1); hence they are called His "council of the holy ones" (Ps. lxxxix. 7, R. V.; A. V. "assembly of the saints"). They accompany God as His attendants, when He appears to man (Deut. xxxiii. 2; Job, xxxviii. 7).
This conception was developed after the Exile; and in the Zechariah, angels of various shapes are delegated "to walk to and fro through the earth" in order to find out and report what happens (Zech. vi. 7). Avenging angels are often present in the Scriptures such as the one in II Sam. xxiv. 15, who annihilates thousands.
In the prophetic books, angels appear as representatives of the prophetic spirit, and bring to the prophets God's word. Thus the prophet Haggai was called God's messenger (angel); and it is known that "Malachi" is not a real name, but means "messenger" or "angel". In I Kings, xiii. 18, an angel brought the divine word to the prophet.