Hope this message finds you well and may God be the light that guides you as you walk with this young man.
One of the first thing that you stated is that Satanism is a form of worship, yes it is true Satanism is its own religion. To God is obviously incorrect. Worshipping of Satan is the complete opposite. “And the Lord said: Simon, Simon, behold Satan hath desired to have you, that he may sift you as wheat: But I have prayed for thee, that thy faith fail not: and thou, being once converted, confirm they bretheren”(St. Luke 22:31-32) As we can see in this verse Satan’s intentions are directly against the will of God. The issue with this scripture is that Jesus is saying it and he is still not at the point where he believes in Christ being God.
Also, the idea of Satan being able to repent and return to heaven is one that many have pondered but we can see in scripture how this is impossible. Reason being is the unforgivable sin. It is mentioned 3 times, I believe, in the New Testament. The unforgivable sin being blasphemy against the Holy Spirit. Now, why is it unforgivable since God can forgive all sins? Well, it’s impossible for there to be anything that God can’t forgive. He’s God. A drop of His blood is more than enough to forgive the world of all its sins. So why does it say that it’s unforgivable? Because to be able to commit blasphemy of the Holy Spirit, one must fully understand what the nature of the Holy Spirit is. One must be able to fully grasp and understand who God is. There isn’t a single human being that I can think of that has been able to fully understand who and what the Holy Spirit is. Why? Because we’re human and as humans we will never fully understand God. So any blasphemy against the Holy Spirit will be rooted in ignorance and ignorance is bliss because you are no longer held to that same standard as someone who does know and understand. This now begs the question who can commit this sin. Satan can. He isn’t human and was with God. All the heavenly bodies understand the full meaning of who and what God is. This doesn’t mean they’re as powerful or all knowing, this simply means that they know enough to commit this sin. So Satan and his followers committed this sin. Now, why is it unforgivable? Not because God can’t forgive them, it’s because when you reach that point of full understanding and are still willing to commit blasphemy against God, nothing will make you feel sorry. You fully understood what was happening and you went along with it with no remorse. And that is why Satan will never change. He has a hatred towards God and nothing will ever change his opinion on Him.
Now we can look at the Old Testament for verses on Satan falling out of heaven, the issue being that in the Old Testament Satan isn’t mentioned in the original scripts. He is referred to as adversary and in many English translations has been changed from adversary to Satan.
Here are some verses from the Old Testament in order to help.
“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.”(Isaias 14:12-13)
“And say to him: Thus saith the Lord God: Thou wast the seal of resemblance, full of wisdom, and perfect in beauty. 13Thou wast in the pleasures of the paradise of God: every precious stone teas thy covering: the sardius, the topaz, and the jasper, the chrysolite, and the onyx, and the beryl, the sapphire, and the carbuncle, and the emerald: gold the work of thy beauty: and thy pipes were prepared in the day that thou wast created. 14Thou 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. 15Thou wast perfect in thy ways from the day of thy creation, until iniquity was found in thee. 16By the multitude of thy merchandise, thy inner parts were filled with iniquity, and thou hast sinned: and I cast thee out from the mountain of God, and destroyed thee, O covering cherub, out of the midst of the stones of fire. 17And thy heart was lifted up with thy beauty: thou best lost thy wisdom in thy beauty, I have cast thee to the ground: I have set thee before the face of kings, that they might behold thee.”(Ezechial 28:12-17)
I would also add some verses from Genesis when it comes to the Serpent but I’m not sure how he will take the idea of Satan being a Serpent.
Hope this helps, if you need any help let me know.
Pax et Bonum