In The Church of Jesus Christ of Latter-day Saints this makes sense since it is the purpose of God to allow his children to progress to become like himself. First and foremost, we believe that there is a component of mankind that is as eternal as God himself. That component is our intelligence. Latter-day revelation reveals that our intelligence was never created or made and neither indeed can be. We have always existed as an intelligence.
Doctrine and Covenants 93:29
29 Man was also in the beginning with God. Intelligence, or the light of truth, was not created or made, neither indeed can be.
Although our intelligences are eternal in nature, God knew that combining elements with intelligence would give the intelligences greater joy. Thus through the process of procreation, God the Father gave birth to our spirits and we became the offspring of God. This spiritual birth combined spirit matter with our intelligences to create our spirit bodies which are also in the likeness of God himself.
Doctrine and Covenants 93:33
33 For man is spirit. The elements are eternal, and spirit and element, inseparably connected, receive a fulness of joy;
34 And when separated, man cannot receive a fulness of joy.
Acts 17:28-29
28 For in him we live, and move, and have our being; as certain also of your own poets have said, For we are also his offspring.
29 Forasmuch then as we are the offspring of God, we ought not to think that the Godhead is like unto gold, or silver, or stone, graven by art and man’s device.
Hebrews 12:9
9 Furthermore we have had fathers of our flesh which corrected us, and we gave them reverence: shall we not much rather be in subjection unto the Father of spirits, and live?
Even though our intelligences are eternal in nature, they are not equal in wisdom, knowledge, understanding, etc. God is a being who has achieved all wisdom, knowledge, understanding, etc. In order to allow his spirit children to become more like himself, he has created this temporary world where our spirits can come and receive more joy by being joined to more physical element known as our physical bodies and he has also provide this temporary fallen world so that we might experience good and evil in order to learn the difference and have the opportunity to choose for ourselves good over evil.
Abraham 3:19
19 And the Lord said unto me: These two facts do exist, that there are two spirits, one being more intelligent than the other; there shall be another more intelligent than they; I am the Lord thy God, I am more intelligent than they all.
Knowing that the intelligences that he made his children from were less intelligence than himself, God provided a means whereby we could all advance. Coming to a knowledge of good and evil and learning to choose evil over good is the means whereby we can advance. Since God could not create our intelligence, he could not create them perfect. They had to
learn to advance to become perfect. That is the purpose of this life.
Genesis 3:22
22 And the Lord God said, Behold, the man is become as one of us, to know good and evil: and now, lest he put forth his hand, and take also of the tree of life, and eat, and live for ever:
In this verse we read that by coming to know good from evil we advance to become like one of the Gods. It was God's purpose that the fall occur and that we enter a temporary world where we could learn good and evil and learn to choose good over evil. We become more knowledgeable by experiencing this life and its good and evil.
Lucifer was a high standing son of God in the premortal world of spirits. However, he was also a very prideful individual. He even wished to be more like God our Father. When God the Father presented the plan for us to come to this earth and be given our free agency to choose good over evil, Lucifer understood that given free will, many would not come back into the presence of God because many would choose evil over good. So Lucifer gave this all a great deal of thought and he proposed his own plan to save mankind. His plan was to take away the free agency of man and force everyone to be obedient. In this way he believed that he would be able to save all mankind and that his plan was greater than the plan of God's. In his pride he took his plan before God the Father but the Father rejected it. The reason the Father rejected Lucifer's plan was because free will is extremely critical to the Father's plan of salvation. In order for a being to truly progress and advance in becoming a truly good being in and of himself, it is critical that they learn to choose good over evil in and of themselves. Otherwise all you really produce is obedient robots. God is a being of free will. He chooses to be good of his own free will and choice. Only in this way is truly a good being. When Lucifer was rejected, his pride got the best of him. He still believed in his plan and he went out among the rest of the children of God and began to recruit others to follow him. He was quite successful and in the end he managed to convince 1/3 of all the hosts of heaven to follow after his plan. This was the war in heaven. It was a war over which plan of salvation the children of God wanted to follow. Those who followed after Lucifer's plan were then denied the opportunity of coming down to earth to receive a mortal body and were to remain as spirits for all eternity. However, God would use Lucifer and his followers on this earth to tempt mankind to test them to see if they would choose good over evil. God would not allow Lucifer to tempt mankind above what they were able to resist, but mankind was allowed to have his free will so that he might choose in of himself what he would list to obey. Thus Lucifer's name was changed to Perdition, Satan, and the devil and his followers became his demons. Our spirits, as the offspring of God are immortal and cannot be destroyed. Thus Satan and his followers cannot be destroyed. But they are serving a purpose here on the earth to try our spirits to see what we will choose. In the end, Satan and his followers will be cast into outer darkness, hell, or also known as the lake of fire and brimstone. It is really just a place without glory where they will contemplate their evil choices for eternity.
But those who learn to choose good over evil will become much wiser, knowledgeable, and more like God and be truly good beings in and of themselves.
Isaiah 14:12-17
12 How art thou fallen from heaven, O Lucifer, son of the morning! how art thou cut down to the ground, which didst weaken the nations!
13 For thou hast said in thine heart,
I will ascend into heaven, I will exalt my throne above the stars of God: I will sit also upon the mount of the congregation, in the sides of the north:
14 I will ascend above the heights of the clouds; I will be like the most High.
15 Yet thou shalt be brought down to hell, to the sides of the pit.
16 They that see thee shall narrowly look upon thee, and consider thee, saying, Is this the man that made the earth to tremble, that did shake kingdoms;
17 That made the world as a wilderness, and destroyed the cities thereof; that opened not the house of his prisoners?
Revelation 12:3-4, 7-11
3 And there appeared another wonder in heaven; and behold a great red dragon, having seven heads and ten horns, and seven crowns upon his heads.
4 And his tail drew the third part of the stars of heaven, and did cast them to the earth: and the dragon stood before the woman which was ready to be delivered, for to devour her child as soon as it was born.
7 And there was war in heaven: Michael and his angels fought against the dragon; and the dragon fought and his angels,
8 And prevailed not; neither was their place found any more in heaven.
9 And the great dragon was cast out, that old serpent, called the Devil, and Satan, which deceiveth the whole world: he was cast out into the earth, and his angels were cast out with him.
10 And I heard a loud voice saying in heaven, Now is come salvation, and strength, and the kingdom of our God, and the power of his Christ: for the accuser of our brethren is cast down, which accused
them before our God day and night.
11 And
they overcame him by the blood of the Lamb, and by the word of their testimony; and they loved not their lives unto the death.
Here we see that the they who fought against the Devil and his angels, came to earth and had to overcome Satan by the blood of lamb and their testimony and they were subject to death. Yes, we fought against Lucifer and his minions in the war in heaven and we are now able to gain a body of flesh and bones and overcome Satan through the blood of lamb and we will all experience death but eventually, thanks be to God the Father and our Savior Jesus Christ, we will all be resurrected to immortal bodies of flesh and bone to live forever and ever.
