In both Old and New Testaments the word "angel" means "messenger". The word is used of both God's messengers and ordinary men. A selection of verses telling us about the work of God's messengers.
Abraham tells his servant that God's angel will prepare the way before him and ensure God's promise is kept:
6 Abraham said to him, “Beware that you don’t bring my son there again. 7 The LORD, the God of heaven—who took me from my father’s house, and from the land of my birth, who spoke to me, and who swore to me, saying, ‘I will give this land to your offspring—he will send his angel before you, and you shall take a wife for my son from there.
God tells the early Israelites that an angel will ensure that God's plan will be carried out:
20 “Behold, I send an angel before you, to keep you by the way, and to bring you into the place which I have prepared.
The psalmist tells us that the angels help those who fear God:
7 The LORD’s angel encamps around those who fear him,
and delivers them.
11 For he will put his angels in charge of you,
to guard you in all your ways.
The psalmist also tells us that the angels obey God’s word and do his will:
20 Praise the LORD, you angels of his,
who are mighty in strength, who fulfil his word,
obeying the voice of his word.
21 Praise the LORD, all you armies of his,
you servants of his, who do his pleasure.
Jesus Christ says that his little ones have their angels who see God's face:
10 See that you don’t despise one of these little ones, for I tell you that in heaven their angels always see the face of my Father who is in heaven.
The letter to the Hebrews tells us that the angels do service for the sake of those who will be saved:
13 But which of the angels has he told at any time,
“Sit at my right hand,
until I make your enemies the footstool of your feet?”
14 Aren’t they all serving spirits, sent out to do service for the sake of those who will inherit salvation?