Therefore, just as through one man sin entered into the world, and death through sin, and so death spread to all men, because all sinned -- for until the Law sin was in the world, but sin is not imputed when there is no law. Nevertheless death reigned from Adam until Moses, even over those who had not sinned in the likeness of the offense of Adam, who is a type of Him who was to come.
The Holy Bible, Romans 5:12-14 (NAS)

In one of the most enigmatic passages in the entire book, Paul sets out to show how one man's death can provide salvation for many. To prove his point, he uses Adam to establish the principle that it is possible for one man's actions to inexorably affect many other people.

Not a particular sin, but the inherent propensity to sin entered the human realm; men became sinners by nature. Adam passed to all his descendants the inherent sinful nature he possessed because of his first disobedience. That nature is present from the moment of conception (Ps. 51- 5), making it impossible for man to live in a way that pleases God. Satan, the father of sin (1 John 3:8), first brought temptation to Adam and Eve (Gen. 3:1-7).

When Adam sinned, all mankind sinned in his loins (v.18; cf. Heb. 7:7-10). Since his sin transformed his inner nature and brought spiritual death and depravity, that sinful nature would be passed on seminally to his posterity as well (Ps.51:5).

Adam, was not originally subject to death, but through his sin it became a grim certainty for him and his posterity. Death has 3 distinct manifestations: 1) spiritual death of separation from God (cf. Eph. 1:1,2; 4:18); 2) physical death (Heb. 9:27); and 3) eternal death (also called the second death), which includes not only eternal separation from God, but eternal torment in the lake of fire (Rev. 20:11-15).

Because all humanity existed in the loins of Adam, and have through procreation inherited his fallenness and depravity, it can be said that all sinned in him. Therefore, humans are not sinners because they sin, but rather they sin because they are sinners.

Though all men were regarded as sinners (v. 12), because there was no explicit list of commands, there was no strict accounting of their specific points of violation during the period from Adam to Moses, when God had not yet given the Mosaic law.

But even without the law, death was universal. All men from Adam to Moses were subject to death, not because of their sinful acts against the Mosaic law (which they did not yet have), but because of their own inherited sinful nature.

[They are] Those who had no specific revelation as did Adam (Gen. 2:16, 17) or those who had the Mosaic law (cf. v.13), but nevertheless sinned against the holiness of God, i.e., those who "sinned without law" (2:12).

Both Adam and Christ were similar in that their acts affected many others. This phrase serves as [a] transition from the apostle's discussion of the transference of Adam's sin to the crediting of Christ's righteousness.
The MacArthur Study Bible, John MacArthur, editor, commentary on Romans 5:12- 14

Will you keep to the ancient path which wicked men have trod, who were snatched away before their time, whose foundations were washed away by a river? They said to God, "Depart from us!" And "What can the Almighty do to them?"
The Holy Bible, Job 22:15-17 (NAS)

They say to God, "Depart from us! We do not even desire the knowledge of Your ways. Who is the Almighty, that we should serve Him, and what would we gain if we entreat Him?"
The Holy Bible, Job 21:14-15 (NAS)

But your iniquities have made a separation between you and your god, and your sins have hidden His face from you so that He does not hear.
The Holy Bible, Isaiah 59:2 (NAS)

"Behold, all souls are Mine; the soul of the father as well as the soul of the son is Mine. The soul who sins will die."
The Holy Bible, Ezekiel 18:4 (NAS)

"The person who sins will die. The son will not bear the punishment of the father's iniquity, nor will the father bear the punishment for the son's iniquity; the righteousness of the righteous will be upon himself, and the wickedness of the wicked will be upon himself."
The Holy Bible, Ezekiel 18:20 (NAS)

For the wages of sin is death, but the free gift of God is eternal life in Christ Jesus our Lord."
The Holy Bible, Romans 6:23 (NAS)

To Adam He said, "Because you listened to your wife and ate from the tree about which I commanded you, 'You must not eat of it,' cursed is the ground because of you; through painful toil you will eat of it all the days of your life. It will produce thorns and thistles for you and you will eat the plants of the field. By the sweat of your brow you will eat your food until you return to the ground, since from it you were taken; for dust you are and to dust you will return."
The Holy Bible, Genesis 3:17-19 (NIV)

So the Lord God banished him from the Garden of Eden to work the ground from which he had been taken.
The Holy Bible, Genesis 3:23 (NIV)

But your iniquities have separated you from your god; your sins have hidden his face from you, so that He will not hear.
The Holy Bible, Isaiah 59:2 (NIV)

"Meaningless! Meaningless!" says the Teacher."Utterly meaningless! Everything is meaningless."
The Holy Bible, Ecclesiastes 1:2 (NIV)

In the morning you will say, "If only it were evening!" and in the evening, "If only it were morning!" - because of the terror that will fill your hearts and the sights that your eyes will see.
The Holy Bible, Deuteronomy 28:67 (NIV)

God who is by nature a deliverer, the only deliverer, has a deliverance plan by which He will deliver the sinner from all those things that damn him. In fact, there may be no better way to understand the power of God's Spirit in the believing sinner's life than to understand that the Spirit is working a work of deliverance. When we talk about conversion and when we talk about regeneration, when we talk about new birth, being born again, new life, transformation...when we talk about these matters of grace we are really talking about being delivered from certain things. In fact, deliverance...defines what it means to be a Christian.
Deliverance: The Neglected Doctrine, John MacArthur

"As Moses lifted up the serpent in the wilderness, even so must the Son of Man be lifted up; so that whoever believes will in Him have eternal life. For God so loved the world, that He gave His only begotten Son, that whoever believes in Him shall not perish, but have eternal life. For God did not send the son into the world to judge the world, but that the world might be saved through Him. He who believes in Him is not judged; he who does not believe has been judged already, because he has not believed in the name of the only begotten Son of God."
The Holy Bible, John 3:14-18 (NAS)

"The person who sins will die. The son will not bear the punishment for the father's iniquity; the righteousness of the righteous will be upon himself, and the wickedness of the wicked will be upon himself."
The Holy Bible, Ezekiel 18:20 (NIV)

For the wages of sin is death, but the gift of God is eternal life in Christ Jesus our Lord.
The Holy Bible, Roman 6:23 (NAS)