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"Believer" is a characteristic of a person who has believed God, has perceived the Revelations of His Covenants, His Will, has felt and realized the need to fulfill God's Commandments, and has become convinced that only their fulfillment achieves the true Good of living in righteousness.
Negative Meaning.
"Believer" is a person who is able to acknowledge the existence of the Creator, God, His Laws and Commandments, but who does not live according to them.
"Unbeliever" is a person who does not believe in the existence of his Creator, who does not realize that only Jehovah God is the One Creator and Ruler of all that exists, that his way of life depends on the fulfillment of His Commandments.
"Unbeliever" is also a person who knows the Will of God, but denies, does not believe in its truth, its goodness, the necessity of obeying God's Commandments as expressed in the Teachings of Jesus Christ.