Adam was tempted by Satan, and made a conscious decision to disobey God.As a result of his choice, Adam lost his righteous standing with God, and became morally corrupt in his nature. This corruption in Adam's nature brought about his spiritual death and spiritual separation from God. Consequently, this moral corruption was passed to all his posterity, and we, as descendants from Adam, have inherited the nature of sin.
Wherefore, as by one man sin entered into the world, and death by sin; and so death passed upon all men, for that all have sinned: Romans 5:12
Now the works of the flesh are manifest, which are these; Adultery, fornication, uncleanness, lasciviousness, Idolatry, witchcraft, hatred, variance, emulations, wrath, strife, seditions, heresies, Envyings, murders, drunkenness, revellings, and such like: of the which I tell you before, as I have also told you in time past, that they which do such things shall not inherit the kingdom of God. Galatians 5:19-21
God has given every human being the freedom to choose good or evil, and holds each one of us accountable for our actions. Because of our inherited sinful nature, we do not have the spiritual power to continually choose good and to please God. To counteract this sinful nature and to bring man into a savable state, God, in his infinite love, brought Jesus Christ into the world for the purpose of redeeming mankind.
For God so loved the world, that he gave his only begotten Son, that whosoever believeth in him should not perish, but have everlasting life. For God sent not his Son into the world to condemn the world; but that the world through him might be saved. John 3:16-17
Forasmuch as ye know that ye were not redeemed with corruptible things, as silver and gold, from your vain conversation received by tradition from your fathers; But with the precious blood of Christ, as of a lamb without blemish and without spot: I Peter 1:18-19
By his death on the cross, Jesus Christ made himself a sufficient sacrifice, oblation and satisfaction for the sin of the whole world. The power of the Holy Spirit strives with and enlightens all men, thus putting them into a savable state. This power is not inherent in any man's nature, but is graciously bestowed on him by God. Therefore, every human soul that chooses to serve God may be saved from the sinful nature, and be restored to a righteous standing with God.
For by grace are ye saved through faith; and that not of yourselves: it is the gift of God: Ephesians 2:8
But without faith it is impossible to please him: for he that cometh to God must believe that he is, and that he is a rewarder of them that diligently seek him. Hebrews 11:6