John 3:16 tells us that God's love for us is so great that He gave His Son, Jesus, to die for us. He did this so that all who believe in Jesus are able to have eternal life with Him in heaven. God has provided the means for our salvation. What is required on our part is to believe and declare.
It is with our hearts and our mouths that we accept God's gracious gift of salvation (Romans 10:9-10). In our hearts, we must not only believe that Jesus is the Son of God, but also that He died for our sins and was raised from the dead. In doing this, Jesus conquered death and restored us to eternal life. When we truly believe this in our hearts, we are justified in God's eyes. We must then use our mouths to declare our faith, our belief that Jesus is Lord and that He died and was raised again. When we believe this with our hearts and declare it with our mouths, we will be saved.