12 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— 13 for [h]until the Law sin was in the world, but sin is not imputed when there is no law. 14 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 [i]type of Him who was to come. Romans 5:12-14
The one who death entered the world through that the apostle Paul writes about is through Adam. When Adam and Eve were created they were perfect. But when they sin, death entered into the human race. People not only would physically face death, but spiritually they would face death in being separated from Almighty God. For God is holy and He cannot be in the presence of sin.
Before the law was given by Moses from God, sin was not imputed because sin cannot be imputed unless the law stands. But when the law came it revealed man’s need of a savior. It demonstrated the righteousness of God and demonstrated man’s inability to keep the law. There is only one who has kept the law perfectly and that is Jesus Christ. Because Jesus came to fulfill the law and not destroy it, His blood becomes the perfect sacrifice to cover and pay the price that exist for sin. As humans we are not able to save ourselves or pay the debt we owe because of sin, but God in His grace and mercy has sent His own Son who has given His life to save us.
Even though sins could not be imputed until the law was put into place. From the time of Adam to Moses humanity faced death. The reasons this is is because if humanity in their sin and degradation were to live forever, there would be no hope of redemption. But God in His mercy limited the life of man upon the earth as man through the fear of death would seek a solution. Many in this world are fearful of death who do not know Jesus Christ. It is our fear of death that when presented with the gospel will be the tool used by the Holy Spirit to soften our hearts to the precious blood of Jesus Christ.
But it isn’t until we come to the revelation of the love of God and the truth of Jesus Christ that we truly come to understand our precious need of a Savior and how wonderful and beautiful Christ is. He in His own freewill took the punishment and wrath we deserve because of sin. But when we understand His sacrifice for us we simply desire to give Him all of our lives and lay down our lives for His kingdom.