WHY IS THE CRUCIFIXION AND RESURRECTION OF JESUS RELEVANT TODAY? • To answer this question, we need to start before the world was ever created: We are told that the Lamb of God, Jesus, was slain from (or before) the foundation of the world. Thus, it was always in the mind of the Father that Christ would come into the world and die to redeem it. This was not something which was added later, and all creation was designed around this. God would not have created the world without this foreknowledge that when Man sinned, a Savior would be ready to enter the picture in due time. 15 And I will put enmity between thee and the woman, and between thy seed and her seed; it shall bruise thy head, and thou shalt bruise his heel. Genesis 3:15 This is the first prophecy of our redemption ever given, and in only a few words tells the course of human history. The serpent, or Satan, would be at war with the woman, and her offspring. Ultimately, that would be Jesus Christ, who is the offspring of the woman (many generations later, through the Virgin Mary). Note that it is her seed and not Adam’s, since the Holy Spirit came upon Mary and caused her to conceive. This “seed” would crush the head of the serpent, meaning He would destroy Satan, but the serpent would bruise His heel in the process. I take this to be a reference to Christ being nailed to the cross through His heels. For even the Son of man came not to be ministered unto, but to minister, and to give his life a ransom for many. Mark 10:45 If for any reason that had not happened, the result would have been perfectly clear–every human being from the beginning of the world to the end would have been lost for eternity and under the wrath of God. We are not saved by His teachings, wonderful as they may be. We are only saved by a simple exchange: His righteousness for all of our sin. The penalty for sin is death. We are accounted as having died through His death, and we shall be released from death by His resurrection. The debt is paid forever. 2 Dear friends, now we are children of God, and what we will be has not yet been made known. But we know that when Christ appears, we shall be like him, for we shall see him as he is. 3 All who have this hope in him purify themselves, just as he is pure. 1 John 3:2-3 Because of this hope, we look every day for the completion of our salvation, which is the transformation of this body into a glorious eternal body, fit to dwell with Him forever. This was a topic posted several years ago in response to someone's email question. I thought it might be worth putting up again. 
And all that dwell upon the earth shall worship him, whose names are not written in the book of life of the Lamb slain from the foundation of the world. Revelation 13:8
The story of the cross is all through the Old Testament. Isaiah 53 describes it; so does Psalm 22. Many other passages depict it in imagery. Moreover, we are told the life of flesh is in the blood and without the shedding of blood, there is no remission of sins (Hebrews 9:22). It was never an option for Jesus NOT to die, nor could He lay down His life in any manner other than by the cross.
He tells us that it was for this reason He came into the world:
We also know that when He comes, we will be changed into His likeness.
