Question: In James 2:19 the Bible says "Thou believest that there is one God’ thou doest well: the devils also believe and tremble." How can we be saved by believing while they are lost by believing?
Answer: The word "devils" should be "demons," as there is only one devil but myriads of demons. Angels are created beings. Colossians 1:16:
"For by him were all things created, that are in heaven, and that are in earth, visible and invisible..."
When Satan attempted to dethrone God (Isaiah 14:13-17), he tried to get all the heavenly host to follow him, but only one-third did (Revelation 12:4). This sealed their eternal fate in Hell (Matthew 25:41). The most wicked are in Torment today (2 Peter 2:5), awaiting the eternal lake of fire. The one-third are known as demons today. Yes, they know and believe that everything in the Bible is true; but they have believed too late (Matthew 8:29).
In Luke 16, a rich man was an unbeliever, but in Hell he believed, however it was too late. Notice his words in Verse 28,
"For I have five brethren; that he may testify unto them, lest they also come into this place of torment."
There are no unbelievers in Hell, but they believe too late, just like the demons.
"Behold NOW is the day of Salvation."
"Believe in the Lord Jesus Christ (NOW) and thou shalt be saved."