Many reject the resurrection, and in doing so harden their hearts, becoming susceptible to the false prophets in our world. Jesus warned us against false prophets as well, as did Paul and Peter. False prophets have no problem telling their followers that Jesus was not crucified, is not the Christ, was not raised from the dead, and is nothing more than a famous teacher of old.
If there is one aspect of any religion that sets Christianity above and over other religions, it is the resurrection of Jesus Christ. There is no greater claim made in any other religion or off-shoot of Christianity. The resurrection is so vital, that Paul said if it were not true, then Christians were to be most pitied among all men.
Yet, the resurrection is true and it is central to Christianity. You may attend church, you may say you are a Christian, but if you do not believe in the bodily resurrection of Christ, then you are following a false Jesus. For it is through the resurrection that every single claim Jesus made is authenticated to be true. It is through the resurrection that every miracle He performed is authenticated. It is through the resurrection that we know He is the final judge of all mankind. It is through the resurrection that the believer knows we have a future (realized) hope of being with Him in glory. It is through the resurrection that we know He is going to come again and judge all mankind (and with them, all other religions).
This is why Paul goes to such great lengths to show the number of eyewitnesses that saw the risen Savior.
For I delivered to you first of all that which I also received: that Christ died for our sins according to the Scriptures,4 and that He was buried, and that He rose again the third day according to the Scriptures, 5 and that He was seen by Cephas, then by the twelve. 6 After that He was seen by over five hundred brethren at once, of whom the greater part remain to the present, but some have fallen asleep. 7 After that He was seen by James, then by all the apostles. 8 Then last of all He was seen by me also, as by one born out of due time (1 Corinthians 3:3-8).
When Paul penned these words, many of these 500 witnesses were still alive. James was still alive. The apostles were still alive. The point is that his claim could be verified by the original audience. Many had seen the risen Savior or could have spoken to those who did see Him. No other religious leader has such an attestation to their false claims of being taken up to heaven.