This question gets to the essence of what life is all about. God tells us everything we need to know with regard to His salvation plan for mankind in His Book, the Bible, and God explains that assurance of our salvation is indeed possible: 1 John 5:11-13 “And this is the record, that God hath given to us eternal life, and this life is in his Son. He that hath the Son hath life; and he that hath not the Son of God hath not life. These things have I written unto you that believe on the name of the Son of God; that ye may know that ye have eternal life, and that ye may believe on the name of the Son of God.”
We must realize that God does ALL the work of salvation. The Bible teaches that we cannot save ourselves. No church, no religious ritual, no person, and no human effort can save us. Only the work done by the Lord Jesus Christ at the cross and by the Holy Spirit in our hearts can save us. Believing, or having “faith”, in the Lord Jesus Christ is the result of salvation – not the cause of it.
If God has already saved you from eternal damnation, He has put His Spirit within you and resurrected your soul (that is, you became a new creature in Christ); and your spiritual war with God has ended, as God stated in the following verses: Ezekiel 36:26-27 “A new heart also will I give you, and a new spirit will I put within you: and I will take away the stony heart out of your flesh, and I will give you an heart of flesh. And I will put my spirit within you, and cause you to walk in my statutes, and ye shall keep my judgments, and do them.”
In other words: If God has saved you from Hell, the Lord Jesus Christ paid for ALL of your sins with His life so that you now have eternal life, and you made no contribution to your salvation in any way: Titus 3:4-7 “But after that the kindness and love of God our Saviour toward man appeared, Not by works of righteousness which we have done, but according to his mercy he saved us, by the washing of regeneration, and renewing of the Holy Ghost; Which he shed on us abundantly through Jesus Christ our Saviour; That being justified by his grace, we should be made heirs according to the hope of eternal life.”
However, if God does not save you before you die or the Lord Jesus Christ returns in judgment, you will spend eternity in Hell under the wrath of God paying for your own sins. In these two verses, God commands us to evaluate our spiritual condition to determine if we truly have received the gift of eternal life based on what the Bible teaches about salvation: 2 Corinthians 13:5 “Examine yourselves, whether ye be in the faith; prove your own selves. Know ye not your own selves, how that Jesus Christ is in you, except ye be reprobates?”