Just about as basic as faith in God is faith in Christ as man's Savior. God created man without sin and warned him that entering into sin would result in death (Gen. 2:17). The initial death that results from sin is spiritual, a separation from God (Isa. 59:1-2). But, as a further result of sin, God removed man from Eden and access to the tree of life (Gen. 3:22-24). As a consequence, physical death became a reality for all mankind. The scriptures also teach that if man dies physically, while already dead spiritually, then eternal death (condemnation in Hell) will be his lot (Rev. 21:8).
Because of this reality, man needed God to intervene on his behalf, to make a way for mankind to be reconciled to God, to be redeemed from the curse of sin. God did this by sending His Son, Jesus Christ, in the role of Savior (Jn. 3:16). Christ paid the price for the guilt of man's sin by giving His own Life on the cross as the ultimate sacrifice (Rom. 5:8; Heb. 7:27; 9:28). Christ is man's only Savior (Acts 4:12), and faith in Him as Savior is essential to salvation.
The devil is man's adversary (1 Pet. 5:8). He seeks to lead man away from God and to eternal destruction. Sin is the avenue that Satan uses to lead man astray (Rom. 6:23). It was the devil who led mankind into sin in the beginning (Gen. 3:1-7), and he continues to do his work of evil today. As certain as is the reality of God and Christ, just as certain is the reality of the devil.
God has a home prepared in Heaven for the redeemed; the way to that blessed eternal home is through Christ (Jn. 14:1-6). The residence of the devil and those he deceives into following him will be, literally, eternal Hell (Matt. 23:33; Matt. 25:41; Rev. 21:8). God, Christ, the devil, Heaven, Hell... All are fundamental aspects of Christian faith...