For follow-up discussion and general commentary on the topic. Comments are sorted chronologically.
Ephesians 1:13-14. In whom ye also trusted, after ye heard the word of truth, the gospel of your salvation, in whom also after ye believed, ye were sealed by the Holy Spirit of promise. Who is the earnest of our inheritance until the redemption of the purchased possession, unto the praise of His glory.
Ephesians 4:30. And grieve not the Holy Spirit in whom ye are sealed unto the day of redemption.
The Holy Spirit is our guarantee of eternal life. Romans 8:9 Without the Spirit there is no salvation. With the Spirit we have eternal life.
Hebrews 13:5 And be content with such things as ye have, for He hath said, I will never leave you or forsake you.
So now we know that the second be believe on Jesus for the free gift of eternal life, we are sealed by the Holy Spirit of promise and will go to heaven whenever we die.
The gospel of our salvation is given in First Corinthians 15:1-4. That Christ died for our sins, according to the scriptures, that He was buried and rose again on the third day, according to the scriptures.
Romans 3:26-28 For He is the just and the justifier of them that believe in Jesus.
First John 3:9. Whosoever is born of God doeth not commit sin, for His seed, (the Holy Spirit) remaineth in Him, and He cannot sin because he is born of God.
Now we have two births. Our first birth was when we were born into this world. That is our flesh birth.
Our new birth is sinless. The Holy Spirit cannot sin. But we still live in our flesh birth. Now we have two natures. The old one and the new one. That is why First John 1:8 says if we say we have no sin we are deceived and the truth is not in us.
We are all sinners to a degree because the flesh is not saved or made perfect. That is why we all die.
Romans 6:23 For the penalty for sin is death, (the bad news), but the GIFT of God is eternal life, through Jesus Christ our Lord. The gift of God is eternal life and guaranteed by the Holy Spirit who will never leave us or forsake us. That is the good news. Jesus died for sinners.
Once we are born into Gods family through the new birth, we are a child of God forever. John 1:12.
Romans 1:16 For I am not ashamed of the gospel of Christ, for it is the power of God unto salvation to everyone that believeth, to the Jew first, and also to the Greek.
It is the seal of the Holy Spirit that makes John 3:18 true. Believers can no longer be condemned to hell, but unbelievers are condemned already because they have not believed on the name of the Son of God.
Second Timothy 2:13 If we believe not, He abideth faithful, He cannot deny Himself. Once we have believed and received the Holy Spirit He abides in us forever even if we lose our faith.
Second Timothy 2:19. Nevertheless, the foundation of God is sure, having this SEAL, the Holy Spirit, the Lord knoweth them that are His. God knows His sheep because we have His Holy Spirit in us.