You don't have a Verse that says what you believe if someone becomes a Satanist they are still saved.
Why would I need a verse specifying anything?
Why don't you believe what Jesus said about who possesses eternal life ans WHEN they do? Jn 5:24
The, why don't you believe what Jesus said about recipients of eternal life? Jn 10:28
With clear verses such as these, it should be obvious that there is NO activity than can remove one's salvation.
Paul said if they remain!
Becoming a Satanist is not remaining.
OK, what is the context. What IF "they remain"? Does the verse say the person who remains will remain saved? Of course it doesn't
Again, you do not have verses that SAY that salvation can be lost.
otoh, I have shown you verses that SAY that recipients of eternal life shall never perish.
Now, can you admit that if a person believed in Christ, then some time later on, for whatever reason, left the faith for whatever else, that recipient of eternal life shall never perish?
btw, I'm not advocating for anyone leaving the faith. They will pay a dear price, though it won't include loss of salvation.
What will be lost is God's blessings, God's protection, fellowship with God, and rewards in eternity.
Oh, and what it WILL GAIN is God's hand of discipline, which will be painful. Heb 12:11.
Too many Arminians opine that if salvation is secure, believers will "get away" with sin.