Jesus said to her, “I am the resurrection and the life. Whoever believes in me, though he die, yet shall he live, and everyone who lives and believes in me shall never die. Do you believe this?”
She said to him, “Yes, Lord; I believe that you are the Christ, the Son of God, who is coming into the world.
When she had said this, she went and called her sister Mary, saying in private, “The Teacher is here and is calling for you.” (John 11:25-28)
This is an emotional moment, Lazarus is dead, why didn't Jesus come sooner. Jesus is wanting Martha to look past the feelings, the situation, he wants her to believe, to have faith, that he is the resurrection and life. He asks Martha do you believe this? Martha replies Yes, you are the Christ, son of God. This is the gospel simple.
Paul states in Romans 10:8-10, that if we confess that Jesus Christ is Lord and believe in our hearts that he was raised from the dead, we shall be saved. Believing is knowing Jesus Christ, he is the resurrection and life, the word which as with God and was God, the bread of life and living water, eternal life (John 1:1,14; 6:35, 7:38). He is also lord and teacher.