Faith in Jesus Christ causes eternal life for our soul and spirit. Jesus not only gives life, but he is life itself. In order to receive spiritual life, a person must first die and then be resurrected and reborn. First we have to die to the sinful life of the past, then comes the resurrection and then life. Jesus gave Lazarus new physical life to show that he has the power to give a new spiritual life. In order to show that he can rescue people from spiritual death and give them spiritual life, he brought Lazarus back from physical death to physical life.
Then Jesus said to Martha that everyone who believes in him, even if he dies, he will live. A believer's body dies, but his soul and spirit do not die. Physical death is only the door to eternal life.