However, before we answer the question, “Why did Jesus have to die?” it’s also important to understand that Jesus clearly understood his mission on earth involved laying down his life as a sacrifice. In other words, Jesus knew it was His Father’s will for him to lay down his life for the mankind.
He proves his foreknowledge and understanding of his death in these passages from Scripture:
Mark 8:31
He then began to teach them that the Son of Man must suffer many things and be rejected by the elders, the chief priests and the teachers of the law, and that he must be killed and after three days rise again. (See also Mark 9:31)
Mark 10:32-34
They were on their way up to Jerusalem, with Jesus leading the way, and the disciples were astonished, while those who followed were afraid. Again he took the Twelve aside and told them what was going to happen to him. ³³ “We are going up to Jerusalem,” he said, “and the Son of Man will be delivered over to the chief priests and the teachers of the law. They will condemn him to death and will hand him over to the Gentiles, ³⁴ who will mock him and spit on him, flog him and kill him. Three days later he will rise.”
Mark 10: 38
“You don’t know what you are asking,” Jesus said. “Can you drink the cup I drink or be baptized with the baptism I am baptized with?”
Mark 10:43-45
Not so with you. Instead, whoever wants to become great among you must be your servant, ⁴⁴ and whoever wants to be first must be slave of all. ⁴⁵ For even the Son of Man did not come to be served, but to serve, and to give his life as a ransom for many.”
Mark 14:22-25
While they were eating, Jesus took bread, and when he had given thanks, he broke it and gave it to his disciples, saying, “Take it; this is my body.” ²³ Then he took a cup, and when he had given thanks, he gave it to them, and they all drank from it. ²⁴ “This is my blood of the^[a] covenant, which is poured out for many,” he said to them. ²⁵ “Truly I tell you, I will not drink again from the fruit of the vine until that day when I drink it new in the kingdom of God.”
John 10:17-18
The reason my Father loves me is that I lay down my life—only to take it up again. ¹⁸ No one takes it from me, but I lay it down of my own accord. I have authority to lay it down and authority to take it up again. This command I received from my Father.”
This last verse also explains why it is pointless to blame the Jews or the Romans—or anyone else, for that matter, for “killing” Jesus. Jesus, having the power to “lay it down” or “take it again,” freely gave up his life. It truly doesn’t matter then, who “killed” Jesus. The ones who nailed the nails only helped carry out the destiny he came to fulfill by laying down his life on the cross.

God is Holy

Though God is all merciful, all powerful and all forgiving, God is also holy, righteous and just.
Isaiah 5:16
But the LORD Almighty will be exalted by his justice, and the holy God will be proved holy by his righteous acts.

Sin and Holiness are Incompatible

Sin entered the world through one man’s disobedience – Adam, and now all of us are born into this “sin nature.”
Romans 5:12
Therefore, just as sin entered the world through one man, and death through sin, and in this way death came to all people, because all sinned
Romans 3:23
for all have sinned and fall short of the glory of God

Sin Separates Us from God

Isaiah 35:8
And a highway will be there; it will be called the Way of Holiness; it will be for those who walk on that Way. The unclean will not journey on it; wicked fools will not go about on it.
Isaiah 59:2
But your iniquities have separated you from your God; your sins have hidden his face from you, so that he will not hear.

Sin’s punishment is Eternal Death

God’s holiness and justice demand that sin and rebellion be punished. The only penalty or payment for sin is eternal Death.

Romans 6:23
For the wages of sin is death, but the gift of God is eternal life in Christ Jesus our Lord.
Romans 5:21
so that, just as sin reigned in death, so also grace might reign through righteousness to bring eternal life through Jesus Christ our Lord.

Atoning Sacrifice

Our death is not sufficient to atone for sin because atonement requires a perfect, spotless sacrifice, offered in just the right way. Jesus, the one perfect God-man, came to offer the pure, complete and everlasting sacrifice to remove, atone, and make eternal payment for our sin.
1 Peter 1:18-19
For you know that it was not with perishable things such as silver or gold that you were redeemed from the empty way of life handed down to you from your ancestors, ¹⁹ but with the precious blood of Christ, a lamb without blemish or defect.
Hebrews 2:14-17
Since the children have flesh and blood, he too shared in their humanity so that by his death he might break the power of him who holds the power of death—that is, the devil— ¹⁵ and free those who all their lives were held in slavery by their fear of death. ¹⁶ For surely it is not angels he helps, but Abraham’s descendants. ¹⁷ For this reason he had to be made like them, fully human in every way, in order that he might become a merciful and faithful high priest in service to God, and that he might make atonement for the sins of the people.

Only Through Jesus Christ

Only through Jesus Christ can our sins be forgiven, thus restoring our relationship with God and removing the separation caused by sin.
2 Corinthians 5:21
God made him who had no sin to be sin for us, so that in him we might become the righteousness of God.
1 Corinthians 1:30
It is because of him that you are in Christ Jesus, who has become for us wisdom from God—that is, our righteousness, holiness and redemption.

The Messiah – Savior

The suffering and the glory of the coming Messiah was foretold in Isaiah 52 and 53. God’s people in the Old Testament looked forward to the Messiah that would save them from their sin. Though he did not come in the form they expected, still their faith looking forward to his salvation saved them. Our faith, looking backward to his act of salvation, saves us. When we accept Jesus’ payment for our sin, his perfect sacrifice washes away our sin and restores our right standing with God. God’s mercy and grace provided a way for our salvation.
Romans 5:10
For if, while we were God’s enemies, we were reconciled to him through the death of his Son, how much more, having been reconciled, shall we be saved through his life!
In Summary, when we are “in Christ Jesus” we are covered by his blood through his sacrificial death, our sins are paid for, and we no longer have to die an eternal death. We receive eternal life though Jesus Christ. And this is why Jesus had to die.