Demons are fallen angels, Jesus' sacrifice was not for them (Hebrews 2:16). Salvation is the full remission of sins and imputation of righteousness according to Jesus' sacrifice (Ephesians 1:7), and belief is the trusting in exactly that (Romans 10:9).
It's all put very clearly in the bible.
We are told we are given eternal life when believing on Jesus:
1 John 5:13
I write these things to you who believe in the name of the Son of God so that you may know that you have eternal life.
Eternal life is received once you believe. You can have it now if you trust in Jesus' sacrifice alone.
@AquaSomethingOx@BrandonLansdown >Taqiyya is an Islamic term referring to the practice of concealing one's religious beliefs or identity to avoid imminent danger, persecution, or severe harm.