To understand this correctly, we have to look at the story of Adam and Eve. Eve ate the fruit and then gave it to her husband Adam who also ate of the forbidden fruit. Both of them knew what God had told them.
In the day they eat it, they would die. It doesn't mean that they instantly fall over dead like food poisoning, but the day they ate of it, they died spiritually. They sinned and were separated from God, and this was the "Fall" and it's important to understand that Adam is not only the first human, but is also a picture of Christ.
Paul tells us that in the same way that one by one man's sin - Adam - it brought death to all mankind, so also the sacrificial death of Christ was our atonement that was the ransom for all mankind.
Christ gave his life and was the 'scape goat' - he willingly gave His life for ours, and it says in Hebrews that He tasted death for every man.
He is not willing that any should perish/ die, but for all to come to repentence.
2 Peter 3:9 English Standard Version
"The Lord is not slow to fulfill his promise as some count slowness, but is patient toward you, not wishing that any should perish, but that all should reach repentance." Christ's sacrificial death on the cross was the ransom for all mankind, but man still has free will, and God doesn't force people to love him. His last words on the cross was "Tetelestai" and this was a widely-used term of accounting in the 1st Century, and it literally means "Paid in full".
Mankind was created with free will. Adam's sin, caused us all to be infected with the sin nature - inborn sin, or Adamic nature, and this broke God's heart so much that he sent his only son to die in our place.
But we do see Jesus, who was made lower than the angels for a little while, now crowned with glory and honor because he suffered death, so that by the grace of God he might taste death for everyone. - (Hebrews 2:9 New International Version)