In fellowship the passed two weeks we have talked about resurrection. Paul stated in 1Corinthians 15:6 that over 500 people saw Jesus alive after His crucifixion. That was Paul's proof that the accounts in the gospels were true regarding the resurrection.
When Christians center their faith ONLY on the cross (important as it is), many miss the fact that Christ's resurrection is the seal of the covenant. Through the power that raised Jesus out of hell (where He was being tormented for OUR sins), believers are transformed into new creations.
Looking at the third chapter of John, notice that Jesus is talking about being "born again" in the spirit-part of the inner man (John 3:5-6). We are saved by believing what God said about the "serpent" who was lifted up on the pole. The New Covenant includes a heart replacement upon which God writes His law and commands. He then works out that salvation as we present our bodies living sacrifices and as we renew our minds with the precepts of the Kingdom.
The cross is where Jesus BEGAN to pay for our sins. He willingly let Himself be put there. He purposefully embraced sin even though He never committed any Himself. And He fully expected the Father to keep the promises regarding deliverance from hell.
Without the resurrection, we would not know that the Father had kept those promises. And we would not see the picture of how we get out of the consequences of our own sin. Cross - Yes. But more so: Cross-Death-Resurrection-Ascension-Return