The resurrection
The book of Acts records the apostle Paul as saying,
"In the past God overlooked such ignorance, but now he commands all people everywhere to repent.
For he has set a day when he will judge the world with justice by the man he has appointed. He has given proof of this to all men by raising him from the dead." Acts 17:30,31
This is a core value of the Christian faith. If you do not believe in the resurrection from the dead then you are not a Christian.
That being said everything around the death and resurrection of Jesus can be a stumbling block for many people. The apostle Paul admits this when he writes to the Corinthians saying,
"Jews demand miraculous signs and Greeks look for wisdom, but we preach Christ crucified: a stumbling block to Jews and foolishness to Gentiles, ...” 1 Corinthians 1:22,23.
The question I would ask those who are not Christians is; considering that the gospel writers were writing about Christ at the very early beginnings of the church. In some cases within living memory of the events. Why would they make a claim that was so, on the surface at least, outrageous.
If the death and resurrection of Jesus was a lie it would certainly turn people away from the fledgeling faith.
Not only that they would have created the most monumental lie in all history. One that is believed by close to three billion people around the world today.
Please think about it.