12 Therefore, just as sin came into the world through one man [Adam], and death through sin, and so death [both physical and spiritual] spread to all men because all sinned—
and death [the death] through sin,
Death is the consequence of Adam’s sin. He was not originally mortal. His spiritual death occurred at the point of his first sin. On the part of human beings, spiritual death occurs at the instant of birth. This is now the situation of all men because man inherited sin capacity directly from him. Adam’s sin is the basis for both universal physical and spiritual death. The fundamental idea of death biblically is separation from God. Physical death is the soul’s separation from the body, and spiritual death is the soul’s separation from God.
The context indicates that death here is more than physical death. Death is joined with “condemnation” (vv. 16, 18) and contrasted to “eternal life” (v. 21). Adam died spiritually on the very day he transgressed God’s command (Ge 2:17) before his ultimate physical death. Upon sinning, he was immediately separated from fellowship with God. Physical death is the result of spiritual death.
Spiritual and eternal death are separation from God.
When Adam sinned he moved from a proper relation to God to alienation from Him; he lost life with God. Men fear physical death today and there is good reason for it. Without God’s provision in Christ, people are hopeless, helpless, and in despair. They view the grave as the dark, dank termination of existence.
Physical and spiritual deaths are one thing but eternal death is another. At the point of physical death, if a person does not trust the death of Christ for his sins, he will spent eternity separate from God.
Christianity offers eternal confidence in the future. Jesus removed the fear of death from those who embrace Him as Savior:
He 2:14 Inasmuch then as the children have partaken of flesh and blood, He Himself likewise shared in the same, that through death He might destroy him who had the power of death, that is, the devil, 15 and release those who through fear of death were all their lifetime subject to bondage.
The unregenerate carries the guilt of eternal death with him while the believer stands justified before God. Eternal death has been defeated in the believer, so he is no longer subject to its power (Ro 8:2). That is why the unregenerate cannot love God with all his heart. He can do good from a human perspective but not from a divine viewpoint. The essence of human perspective is natural instinct, not a regenerate heart. The love of a parent for a child is natural instinct. “Natural inclination” is whatever a fallen person is inclined to do. He is pure soul without orientation to God (1 Co 2:14). This inclination does not come from his birth but from his innate sin capacity/inclination (Ep 2:3).