You're supposed to treat others the way you would want to be treated. Do this throughout your life on earth and you are promised eternal life. Celebrate the gift of life that is given to you and try not to be selfish with your time here. Do this and upon your death you will enter a kingdom where there is no pain, fear, worry, or sorrow.
That all sounds desirable. This man came around 2,000 year ago and told everyone he met these kinds of things. It's no wonder he found a few followers. Since then, millions of those who believed him have lived and passed on, realizing for whether his promises were true or not. For better or worse, we don't know if they proved him right or wrong.
Yet even if it was all false, what the man told us to do to get there really isn't asking for much. In fact, if you have ever done kind things for others and showed compassion to those in need, you more often than not feel good about yourself anyway. Isn't it ironic how you are ultimately serving yourself by serving others?