Angels can be thought of as God’s assistants: Who makes his angels spirits, His ministers a fire (Ps. 104.4 Sept.). The popular conception of angels, chubby infants with wings, is diametrically opposed to the biblical description of them. Often a protective or military aspect is revealed: For he will command his angels concerning you to guard you in all your ways (Ps. 91.11 NRSV). Also, the Archangel and his troops conduct war: Then war broke out in heaven. Michael and his angels fought against the dragon, and the dragon and his angels fought back but he was defeated, and there was no longer any place for them in heaven (Rev. 12.7-8 NIV).
The Septuagint was a Greek translation of the Hebrew Bible (O.T.) translated as early as 3rd century BCE (Torah) and 2nd century BCE (Prophets and writings). It translates the Hebrew term for angel (malakh) into the Greek angelos. Both Hebrew and Greek terms denote the concept of messenger. Therefore, the good angels seem to be messengers of words or deeds from God. Angels are also divided into ordered ranks, which involve hierarchical relationships, as seen by the term “archangel” in places like Jude 9.
Replacing the Fallen Ranks
Peter was Jesus’ initial spokesperson of the nascent Church. He recognized the need to fill the post that Judas deserted among the Twelve to make up that number: Therefore it is necessary to choose one of the men who have been with us the whole time the Lord Jesus was living among us (Acts.1.21 NIV). Peter quotes Ps. 109.2, making the point that a formal and established office existed of those whom Jesus had chosen: Let his days be few, his office, let another take his place of leadership (Acts 1.20b NIV). In the scriptures, it seems that some ministries and offices are meant to be filled to a certain number.
Therefore, it seems that since some angels have fallen, their ranks need to be filled. Earthly life in its ideal form is a reflection of heaven and its relations. God’s court will be populated by a myriad of hosts to bring Him glory just like a human king is honored by many subjects: In a multitude of people is the glory of a king, but without people a prince is ruined (Prov. 14.28 ESV). Additionally, Proverbs tells us that a large army following a King lends stateliness to his procession: Three things are stately in their tread; four are stately in their stride: the lion, which is mightiest among beasts and does not turn back before any; the strutting rooster, the he-goat, and a king whose army is with him (Pr. 30.29-31 ESV).
I have argued that the imprisonment of evil angels that Peter speaks about in 2Pet. 2.4 is best fulfilled by the first day of creation (re-creation) in Gen. 1.2-4: https://beliefspeak2.net/11618-2/?review_id=11618&preview_nonce=27eaa21058&preview=true. If I am correct, then what we see in Genesis, from the first day onward, is a divine plan to raise up replacements for the angels who have fallen. Of course, this is not the exclusive purpose of God in redemption, but another reason to praise our Savior forever.
Angels are Immortal by Nature
It seems that the angels were created with native immortality: and they can no longer die; for they are like the angels (Lk. 20.36a NIV). Humanity contained in Adam (even Eve was created from Adam) was created mortal. This is easily seen by the promise of eternal life set before the first couple by the Tree of Life. If they had native immortality, then the promise of everlasting life would never need to have been made: in the hope of eternal life, which God, who does not lie, promised before the beginning of time (Tit. 1.2 NIV). Paul tells Timothy that the gospel brings immortality; therefore, if humans had any kind of native immortality, Paul’s statement is superfluous: and which now has been manifested through the appearing of our Savior Christ Jesus, who abolished death and brought life and immortality to light through the gospel (2Tim. 1.10 ESV).