Angels Can Not Be Counted
Angels are a host of beings so numerous they can't be counted. We see an awesome picture of this in Daniel's description of God on the throne as Judge: "A river of fire was flowing and coming out from before Him, thousands upon thousands were attending Him, and ten thousand times a hundred thousand stood before him" (Daniel 7:10)
"Ten thousand times a hundred thousand" is another way of saying one hundred million angels. And those were just the ones Daniel saw. Hebrews 12:22 says, "But you are come to mount Sion, and to the city of the living God, the heavenly Jerusalem, and to the company of innumerable angels."
Demons must also exist in vast numbers. Revelation 12:4 indicates that one-third of the angelic host followed Satan in his rebellion. "And there was seen another sign in heaven: and behold a great red dragon, having seven heads, and ten horns: and on his head seven diadems: And his tail drew the third part of the stars of heaven, and cast them to the earth: and the dragon stood before the woman who was ready to be delivered; that, when she should be delivered, he might devour her son."
The sign that is given to us is not literal. When John gives us a symbol, he will make it clear that it is a symbol.
The red dragon is clearly identified as Satan in verse 9: "And that great dragon was cast out, that old serpent, who is called the devil and Satan, who seduceth (or deceives) the whole world; and he was cast unto the earth, and his angels were thrown down with him." The "Third part of the stars of heaven" indicates the vast and innumerable extent of the rebellion in heaven when one third of the angelic host followed Satan to their own destruction.
So Satan and his followers are all angels who chose to reject God's authority and were cast from heaven.
How art thou fallen from heaven, O Lucifer, who didst rise in the morning? how art thou fallen to the earth, that didst wound the nations? And thou saidst in thy heart: I will ascend into heaven, I will exalt my throne above the stars of God, I will sit in the mountain of the covenant, in the sides of the north. I will ascend above the height of the clouds, I will be like the most High. But yet thou shalt be brought down to hell, into the depth of the pit.
Thou a cherub stretched out, and protecting, and I set thee in the holy mountain of God, thou hast walked in the midst of the stones of fire. Thou wast perfect in thy ways from the day of thy creation, until iniquity was found in thee.
Satan was the cherub that "stretched out/covered and protected" the throne of God. This is apparently a picture of heaven itself. so we can see that Satan at one time, before he was Satan and before he had fallen, had access to heaven.
This vast evil host on earth is a key reason you and I need divine help to wage successful spiritual warfare. And Satan is so clever and intelligent that we are no match whatsoever for him in our own strength. But in God's power we can overcome an army!
The number of angels was fixed by God and will not change, both because they do not pro-create, (Matthew 22:30) and because, like our spirits that will live on forever in either heaven or hell, they are eternal beings.
Lastly, let us consider the verse we just mentioned in Saint Matthew.
"For in the resurrection they shall neither marry nor be married; but shall be as the angels of God in heaven." (Matthew 22:30)
The contexts of this verse is that the Sadducees did not believe in the resurrection, They used a ridiculous illustration to try to trap the Lord. Imagine a women who had had seven brothers for her husbands! Their question was, Whose wife shall she be? The Sadducees erred in two respects. Ignorance of Scriptures and ignorance of the power of God. And so the Lord brings this to their attention.
In Matthew 22:30, Jesus is not saying that those in the resurrection, which include us, are angels in heaven. But we will be like angels in that we will not marry in heaven or be given in marriage. In other words their will not be any necessity to continue the race by means of birth.