John 6:27-29 NKJV
Do not labor for the food which perishes, but for the food which endures to everlasting life, which the Son of Man will give you, because God the Father has set His seal on Him.”  Then they said to Him, “What shall we do, that we may work the works of God?”  Jesus answered and said to them, “This is the work of God, that you believe in Him whom He sent.”
John 3:3, 35-36 NKJV
Jesus answered and said to him, “Most assuredly, I say to you, unless one is born again, he cannot see the kingdom of God.”  The Father loves the Son, and has given all things into His hand.  He who believes in the Son has everlasting life; and he who does not believe the Son shall not see life, but the wrath of God abides on him.”
Revelation 21:27 NKJV
But there shall by no means enter it ( Heaven ) anything that defiles, or causes an abomination or a lie, but only those who are written in the Lamb’s Book of Life.
Revelation 20:12-15 NKJV
And I saw the dead, small and great, standing before God, and books were opened. And another book was opened, which is the Book of Life. And the dead were judged according to their works, by the things which were written in the books.  The sea gave up the dead who were in it, and Death and Hades delivered up the dead who were in them. And they were judged, each one according to his works.  Then Death and Hades were cast into the lake of fire. This is the second death.  And anyone not found written in the Book of Life was cast into the lake of fire.