According to Protestantism, why are fallen angels motivated to attack Christians?

From a Protestant perspective, the biblical explanation for why why fallen angels are motivated to attack Christians is simple. Their motivation stems from knowing that their time is short, and they face judgment.

1 Peter 5:8 says: “Your enemy the devil prowls around like a roaring lion looking for someone to devour.”

2 Peter 2:4 says: “God did not spare angels when they sinned, but sent them to hell, putting them into gloomy dungeons to be held for judgment”.

1 Corinthians 6:2-3 says “the saints will judge the world” and “we will judge angels”.

Other Bible verses teach that the fallen angels will be judged by God (Isaiah 24:21-22; 2 Peter 2:4; Jude 6; Revelation 21:10).

That’s why they are hell-bent on attacking God’s people, even though their efforts are futile.

The Bible tells us that the angels were created before the earth (Job 38:4-7) and that Satan fell before he tempted Adam and Eve in the Garden (Genesis 3:1-14). At some later point, he was cast out of heaven.

Isaiah 14:12-15: “How are you fallen from heaven, O Lucifer, son of the morning! How are you cut down to the ground, which did weaken the nations! For you have said in your 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: I will ascend above the heights of the clouds; I will be like the most High. Yet you shall be brought down to hell, to the sides of the pit.”

Jesus said, “I saw Satan fall like lightning from heaven” (Luke 10:18), and in Revelation Satan is seen as “a star that had fallen from the sky to the earth” (Revelation 9:1). Since Satan is referred to as a star which fell or was cast down to earth and Revelation 12:4 says a third of the stars were cast out with him, then the suggestion is that the stars in Revelation chapter 12 refer to fallen angels, fully one third of the heavenly host.

Revelation 12:17 describes how the dragon was enraged and went off to make war against “those who obey God’s commandments and hold to the testimony of Jesus.” Later, Satan is bound and thrown into the Abyss for the duration of the millennial reign of Christ on earth. He is then released for a short while to make a final assault on God’s people before being thrown into the lake of burning sulphur, to be tormented day and night for ever and ever (Revelation 20:1-10).

Satan and all who follow him are not ignorant of what the Bible says about their final end. That is why they are enraged and why, even at the end of the millennial reign of Christ, when Satan is released for a short time, they will wage war against God’s people. Their motivation is hatred for God, for Christ Jesus and for all who follow Him. What caused it was that initial rebellion against God, aspiring to overthrow God – see Isaiah 15:12-15 as quoted above.

I found an article from the Jewish Encyclopedia about The Book of Adam (by Louis Ginzberg) which starts out by saying “The Talmud says nothing about the existence of a Book of Adam...” It continues:

After God had created man, He ordered all the angels to prostrate themselves before Adam, but Satan rebelled against God's command, despite the direct bidding of Michael "to worship the image of YHW."

However, that does not answer your question as to what motivates the fallen angels to attack Christians. After all, this apocryphal book does not concern itself with Christianity. It concludes by suggesting the apocryphas of Mosis and the Vita are based on the Hebrew or Aramaic Book of Adam and that the latter belongs to the midrashic literature, as many of its allusions can only be explained by the Midrash. Source: http://www.jewishencyclopedia.com/articles/759-adam-book-of

I pay no heed to those extra-biblical sources that suggest God told all the angels to bow down and worship Adam. Why would God tell his created angels to worship a created human when the Shema makes it very clear that God alone is to be worshipped? Jesus himself quoted from Deuteronomy 6:4 (in Mark 12:28-30). Hebrews 1:9 commands all God’s angels to worship his Son, not Adam. Hmmm, I can feel a question coming on.....