Greetings FTS,
"Believing" is demonstrated in obedience to that which is to be believed. In other words, if anyone believes the command to do good they will demonstrate their faith in those commands by doing them. Anyone who both knows His commands and keeps them is the "believer". Anyone who opposes His commands has no faith or believes in those commands.
Your question is good! Sadly many boast of their "unbelief".
SG
I believ this to be true, Jesus, James, Revelation all say things along these lines.
James 2:19-20, " 19 You believe that God is one; you do well. Even the demons believe—and shudder! 20 Do you want to be shown, you foolish person, that faith apart from works is useless?
Matthew 21:28-32, " 28 “What do you think? A man had two sons. And he went to the first and said, ‘Son, go and work in the vineyard today.’ 29 And he answered, ‘I will not,’ but afterward he changed his mind and went. 30 And he went to the other son and said the same. And he answered, ‘I go, sir,’ but did not go. 31 Which of the two did the will of his father?” They said, “The first.” Jesus said to them, “Truly, I say to you, the tax collectors and the prostitutes go into the kingdom of God before you. 32 For John came to you in the way of righteousness, and you did not believe him, but the tax collectors and the prostitutes believed him. And even when you saw it, you did not afterward change your minds and believe him.
Revelation 14:12-13, " 12 Here is a call for the endurance of the saints, those who keep the commandments of God and their faith in Jesus. 13 And I heard a voice from heaven saying, “Write this: Blessed are the dead who die in the Lord from now on.” “Blessed indeed,” says the Spirit, “that they may rest from their labors, for their deeds follow them!”