Why Does God Let Satan Exist?
Originally, God created Satan without sin. He was originally in charge of music in heaven; however, after pride entered his heart, it became his undoing. God allows Satan to still exist because He won't do anything until the end of the world. In Isaiah 14:12-15 this what the Bible has to say:
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.
God created Satan as one of His servants. However, Satan was arrogant when he refused to prostrate to Prophet Adam despite the commandment of God. Satan was then thrown out of heaven. He pleaded that God should allow him to live until the end of life in this world. God granted him that. However, God did not give Satan any power to control mankind beyond their freewill. God sent everyone to this world as a vicegerent and warn all that Satan is mankind’s greatest enemy. This is a test from God and every soul has choice to either follow the right track or deviate.
“And [mention] when We said to the angels, "Prostrate to Adam," and they prostrated, except for Iblees. He said, "Should I prostrate to one You created from clay? [Iblees] said, "Do You see this one whom You have honored above me? If You delay me until the Day of Resurrection, I will surely destroy his descendants, except for a few. [Allah] said, "Go, for whoever of them follows you, indeed Hell will be the recompense of you - an ample recompense.” Qur’an 17:61-64
“Indeed, My servants - no authority will you have over them, except those who follow you of the deviators.” Qur’an 15:42
“And Satan will say when the matter has been concluded, "Indeed, Allah had promised you the promise of truth. And I promised you, but I betrayed you. But I had no authority over you except that I invited you, and you responded to me. So do not blame me; but blame yourselves. I cannot be called to your aid, nor can you be called to my aid. Indeed, I deny your association of me [with Allah] before. Indeed, for the wrongdoers is a painful punishment." Qur’an 14:22