Apostle Paul so succinctly wrote this Now I make known to you, brethren, the gospel which I preached to you, which also you received, in which also you stand, by which also you are saved, if you hold fast the word which I preached to you, unless you believed in vain. For I delivered to you as of first importance what I also received, that Christ died for our sins according to the Scriptures, and that He was buried, and that He was raised on the third day according to the Scriptures.[1 Corinthians 15:1-4]
We can see the gospel clearly expressed in these four vss. We can see the cross in this passage as Paul wrote that Christ died for our sins according to the Scriptures. It was even prophesied what type of death He would have when it was written Then the LORD said to Moses, “Make a fiery serpent, and set it on a standard; and it shall come about, that everyone who is bitten, when he looks at it, he will live.” And Moses made a bronze serpent and set it on the standard; and it came about, that if a serpent bit any man, when he looked to the bronze serpent, he lived.[Numbers 21:8-9] We can read of the "Suffering Servant" in Isaiah and know that His death was not any run-of-the-mill death, but a most gruesome death. We can also read And one will say to him, ‘What are these wounds between your arms?’ Then he will say, ‘Those with which I was wounded in the house of my friends.’[Zechariah 13:6] He was even betrayed by one He called 'friend'.[Matthew 26:50]
The reason why we speak of the cross is because the cross is where the payment for His sheep's sins were paid. Without an empty tomb, the cross is null and void. But without the cross, there is no empty tomb, either. We have to get the gospel right, because if we fail to get that right, the rest of our theology is off. That is why we need to see a Trinity in view in the scriptures. It took God to become a man to redeem us. If man could have redeemed us, the Christ wasted His time dying. If the Christ was this good moral man who later became the Messiah, then His sacrifice is useless as well. God could have done that with the likes of Aaron, Moses, David, Solomon, Samson, Eleazer, if that were the case. It took God to become a man to live a sinless, perfect life, live a life that fulfilled every requirement the Law demanded be lived. No created being could do this. It took God to come in the flesh.
Now focusing in on the cross. The cross was where our sin debt was paid in full. There is nothing we can add to this cross. It was God the Son being imputed His sheep's sins,[2 Corinthians 5:21] standing before His Father as our Sinbearer, taking God's wrath, dying our death, atoning for our sins, and raising from the tomb for our justification.[Romans 4:25]. This is a Triune God at work in man's redemption. The only thing His sheep brought to this was their sins that had been laid upon Him. God the Son took God the Father's wrath, so that God the Holy Spirit could now fully come unto the elect. If the cross was for everybody, and everybody was not saved, then the cross, in and of itself, did not save them. That is why we, the Calvinists, can proclaim a cross that has a 100% success rate. The cross was for His sheep, His life He lived and gave, was for His sheep, His resurrection was for His sheep, His intercession is for His sheep, and His second advent is for His sheep.