Jesus Himself said that since I believe, I HAVE eternal life, I do not come into judgment, that I will not perish because no one can take me out of His hand.
He promises that in His word and I don't need to work to get it or keep it.
We're saved by grace through faith in Christ and kept by that same grace.
Security of believer
John 5:24 Truly, truly, I say to you, whoever hears my word and believes him who sent me has eternal life. He does not come into judgment, but has passed from death to life.
John 10:25-30 Jesus answered them, “I told you, and you do not believe. The works that I do in my Father's name bear witness about me, but you do not believe because you are not among my sheep. My sheep hear my voice, and I know them, and they follow me. I give them eternal life, and they will never perish, and no one will snatch them out of my hand. My Father, who has given them to me, is greater than all, and no one is able to snatch them out of the Father's hand. I and the Father are one.”
Ephesians 1:13-14 In him you also, when you heard the word of truth, the gospel of your salvation, and believed in him, were sealed with the promised Holy Spirit, who is the guarantee of our inheritance until we acquire possession of it, to the praise of his glory.
Ephesians 4:30 And do not grieve the Holy Spirit of God, by whom you were sealed for the day of redemption.
Colossians 1:13-14 He has delivered us from the domain of darkness and transferred us to the kingdom of his beloved Son, in whom we have redemption, the forgiveness of sins.
2 Corinthians 1:21-22 And it is God who establishes us with you in Christ, and has anointed us, and who has also put his seal on us and given us his Spirit in our hearts as a guarantee.
2 Corinthians 5:4-8 For while we are still in this tent, we groan, being burdened—not that we would be unclothed, but that we would be further clothed, so that what is mortal may be swallowed up by life. He who has prepared us for this very thing is God, who has given us the Spirit as a guarantee. So we are always of good courage. We know that while we are at home in the body we are away from the Lord, for we walk by faith, not by sight. Yes, we are of good courage, and we would rather be away from the body and at home with the Lord.
Philippians 2:12-13 Therefore, my beloved, as you have always obeyed, so now, not only as in my presence but much more in my absence, work out your own salvation with fear and trembling, for it is God who works in you, both to will and to work for his good pleasure.
So it's not even me having the will to do good works, it comes from God alone. Only quoting the first part of the verse, that we should work out our salvation with fear and trembling and using that as a proof text to justify the doctrine of works based salvation, is a misuse of God's word.
It's all God and only God. Nothing we can do can count towards our salvation, either earning it or keeping it.
Catholicism teaches saved by grace, kept by works. The Bible teaches saved by grace, kept by grace.
Galatians 3:1-6 O foolish Galatians! Who has bewitched you? It was before your eyes that Jesus Christ was publicly portrayed as crucified. Let me ask you only this: Did you receive the Spirit by works of the law or by hearing with faith? Are you so foolish? Having begun by the Spirit, are you now being perfected by the flesh? Did you suffer so many things in vain—if indeed it was in vain? Does he who supplies the Spirit to you and works miracles among you do so by works of the law, or by hearing with faith— just as Abraham “believed God, and it was counted to him as righteousness”?
How sad for those who follow the RCC to not know the promises of God and feel that assurance of the Holy Spirit.
“I am saved and secure in Him, sealed with the promised Holy Spirit as a guarantee of my inheritance until I acquire possession of it.”
Once-saved-always-saved is not an orthodox Christian belief. It is a phony 16th century Protestant invention. Even many Protestants recognize that today. Here’s just one example: http://www.evangelicaloutreach.org/dan-corner-the-believers-conditional-security.htm