Why is the cross the symbol of Christ’s death and resurrection but not the grave?

While the cross certainly has its meaning in the instrument of execution by the Romans of the lowest class of criminals, it has also come to represent the meaning of Christ’s death and the redemption that that death bought for us. Paul speaks of the “message” of the cross; in writing to the church at Corinth, he says, For Christ did not send me to baptize, but to preach the gospel—not with words of human wisdom, lest the cross of Christ be emptied of its power. For the message of the cross is foolishness to those who are perishing, but to us who are being saved it is the power of God—Paul, I Corinthians 1:17-18. It is through Jesus’ death on the cross that Jesus reconciled both Jew and Gentile—in other words, the entire world—to God through that horrific death on the cross. As Paul said to the Ephesian church, [R]emember that at that time you were separate from Christ, excluded from citizenship in Israel and foreigners to the covenants of the promise, without hope and without God in the world. But now in Christ Jesus you who once were far away have been brought near by the blood of Christ. For he himself is our peace, who has made the two one and has destroyed the barrier, the dividing wall of hostility, by abolishing in his flesh the law with its commandments and regulations. His purpose was to create in himself one new man out of the two, thus making peace, and in this one body to reconcile both of them to God through the cross, by which he put to death their hostility. He came and preached peace to you who were far away and peace to those who were near. For through him we both have access to the Father by one Spirit. Consequently, you are no longer foreigners and aliens, but fellow citizens with God’s people and members of God’s household, built on the foundation of the apostles and prophets, with Christ Jesus himself as the chief cornerstone—Paul, Ephesians 2:12-20. The cross not only represents everything to the Christian—it is everything! So when Paul would preach, he was not concerned with the brilliance of his oratory or the passion of his arguments but with the cross of Christ; as he said in the Corinthian church, When I came to you, brothers, I did not come with eloquence or superior wisdom as I proclaimed to you the testimony about God. For I resolved to know nothing while I was with you except Jesus Christ and him crucified. I came to you in weakness and fear, and with much trembling. My message and my preaching were not with wise and persuasive words, but with a demonstration of the Spirit’s power, so that your faith might not rest on men’s wisdom, but on God’s power—Paul, I Corinthians 2:1-5. The cross was Paul’s focus; it had to be. Nobody would try to speak eloquently about a person executed by crucifixion. This was Rome’s most vicious capital punishment, and reserved for the worst criminals in their custody. It was not even to be performed on Roman citizens, so great was its perceived shame on the victim. Yet Christians are to glory in the cross in Christ’s case because it was through the cross that the power of God was revealed to all mankind in His ability to lead people from death to life by means of the atoning, redemptive work done at that horrific place. Without the message of the cross, the effectiveness of the life and death of Christ is rendered meaningless. It is the cross that destroys the hostility—created by sin—between a sinful mankind and a holy, perfect God. The simple fact is that the cross stands for the astonishing fact that God placed Himself into humanity in the person of Jesus Christ and then died the humiliating death of crucifixion in order to bring mankind back to God. The cross becomes an incredibly vivid, graphic, ironic picture—the total absurdity of the shame of the cross becoming the most glorious event in human history due to what was accomplished there and what was offered to us by means of that accomplishment. Because of that, Paul referred to those who opposed his message like this: For, as I have often told you before and now say again even with tears, many live as enemies of the cross of Christ—Paul, Philippians 3:18. Why enemies of “the cross?” Because it was at the cross that everything that man needs to be reconciled with God was accomplished and offered. To deny the cross, to oppose the cross, denies and opposes mankind’s ONLY opportunity and means of salvation. And, during His ministry on earth, Jesus said, If anyone would come after me, he must deny himself and take up his cross daily and follow me. For whoever wants to save his life will lose it, but whoever loses his life for me will save it. What good is it for a man to gain the whole world, and yet lose or forfeit his very self?—Jesus Christ, Luke 9:23-25. This was a picture not necessarily of physical suffering as it was about full submission to the will of God. For Jesus, that meant crucifixion. Whatever it specifically winds up meaning for a Christian, it is the cross that is used by Christ Himself to reflect surrender to whatever God wants. It becomes the modeling of our lives after Christ’s incredible example; as He Himself said in Upper Room, I have set you an example that you should do as I have done for you—Jesus Christ, John 13:15.
Now Paul did speak, with great eloquence, about the power of God displayed in His raising Christ from the dead; as He shared with the church at Corinth, But if it is preached that Christ has been raised from the dead, how can some of you say that there is no resurrection of the dead? If there is no resurrection of the dead, then not even Christ has been raised. And if Christ has not been raised, our preaching is useless and so is your faith. More than that, we are then found to be false witnesses about God, for we have testified about God that he raised Christ from the dead. But he did not raise him if in fact the dead are not raised. For if the dead are not raised, then Christ has not been raised either. And if Christ has not been raised, your faith is futile; you are still in your sins. Then those also who have fallen asleep in Christ are lost. If only for this life we have hope in Christ, we are to be pitied more than all men. But Christ has indeed been raised from the dead, the firstfruits of those who have fallen asleep—Paul, I Corinthians 15:12-20. It is the great hope that all Christians share, that life apart from earth means life forever in heaven—in the presence of God the Father and God the Son, the Lord Jesus Christ. As Christ Himself shared with His disciples in the Upper Room, In my Father’s house are many rooms; if it were not so, I would have told you. I am going there to prepare a place for you. And if I go and prepare a place for you, I will come back and take you to be with me that you also may be where I am—Jesus Christ, John 14:2-3. And certainly the Scriptures point to that promise time and again as the great balance against what we have to deal with in this life; Paul said it so well: [W]e know that the one who raised the Lord Jesus from the dead will also raise us with Jesus and present us with you to himself. All this is for your benefit, so that the grace that is reaching more and more people may cause thanksgiving to overflow to the glory of God. Therefore we do not lose heart. Though outwardly we are wasting away, yet inwardly we are being renewed day by day. For our light and momentary troubles are achieving for us an eternal glory that far outweighs them all. So we fix our eyes not on what is seen, but on what is unseen, since what is seen is temporary, but what is unseen is eternal—Paul, II Corinthians 4:14-18.
But the writings of the New Testament make the focus clear: It is at the cross that Jesus paid the incredibly immense penalty for our sins, our every sin—going so far as to suffer the severing of His relationship with His own Father in the process—so that we could know the magnificence of a restored relationship with God. Paul said it this way to the church at Colossae: For God was pleased to have all his fullness dwell in him, and through him to reconcile to himself all things, whether things on earth or things in heaven, by making peace through his blood, shed on the cross. Once you were alienated from God and were enemies in your minds because of your evil behavior. But now he has reconciled you by Christ’s physical body through death to present you holy in his sight, without blemish and free from accusation—Paul, Colossians 1:19-22. But maybe no words say it better than Christ’s own words on the cross, as He realized that His mission had finally been accomplished: It is finished—Jesus Christ, John 19:30a. So while the grave shows that even death has been conquered, it is at the cross that sin—the result of which is death—has been conquered. That’s why Paul said, May I never boast except in the cross of our Lord Jesus Christ—Paul, Galatians 6:14a.