We are born into a world at war.
The war between good and evil.
Against goodness and God, and those who would rebel against.
We must chose our side and fight! The default is the rebellion.
In humanity's arrogance they sought to decide good and evil on their own terms and separated from the glory that God had destined them for. God is love and justice and goodness. He is the Way, the Truth, and the Life. Paradise lies with God, goodness and peace are with Him. God's patience and mercy is long. You have your whole life to chose and Jesus is waiting long to come back that no one would be separated from Him. God will judge according to your deeds unless you repent and receive salvation in Jesus' name. There will be justice for evil and wrongdoing. One day there will be only goodness on Heaven and Earth.
There are angels that rebelled against God too and left heaven. But unlike the forgiveness, mercy, and restoration God offers humans, there is none for the fallen angel demons.
They hate God and us His creation which He loves. They muck about evil. God will exact justice on them, for now they lie and hurt humans hoping to drag anyone down with them. While their rebellion and evil is in full show, to God's glory He will let it be evident how wrong that path is.
And that is why we must armor up.
10 Finally, be strong in the Lord and in his mighty power. 11 Put on the full armor of God, so that you can take your stand against the devil’s schemes. 12 For our struggle is not against flesh and blood, but against the rulers, against the authorities, against the powers of this dark world and against the spiritual forces of evil in the heavenly realms. 13 Therefore put on the full armor of God, so that when the day of evil comes, you may be able to stand your ground, and after you have done everything, to stand. 14 Stand firm then, with the belt of truth buckled around your waist, with the breastplate of righteousness in place, 15 and with your feet fitted with the readiness that comes from the gospel of peace. 16 In addition to all this, take up the shield of faith, with which you can extinguish all the flaming arrows of the evil one. 17 Take the helmet of salvation and the sword of the Spirit, which is the word of God.