I started my research looking for information about why Protestants believe in Eternal Security. Since there's no collective document nor do I own any books about a particular topic, I turned to the internet. Turns out this theology is controversial among Protestants. Maybe there are some good apologetic Protestant sites on the net, but the few sites I came across used lots of colorful, large font with many exclamation points. Some read "Eternal Security is in the Gospel" and others read "No Eternal Security."
So what did I do? I went and looked it up from a Catholic's prospective. Most Catholic sites are very good about explaining what it is and then explaining why we don't believe in it. So they've done my homework for me. I'm going to briefly explain what it is, site sources that refute the doctrine, and give brief descriptions of how these sites tackle the issue.
Okay: Eternal Security is a Protestant dogma that says that once a person accepts Jesus as Lord, their salvation (ie trip to heaven) is assured. Their salvation cannot be taken from them. It's also quoted as "once saved, always saved." They base this belief on numerous passages in the Bible. I will quote some of these for you along with context since a large part of the reason people disagree with Eternal Security is because of context. I won't quote them all because that would railroad too much of the discussion. If you would like to bring up a different Bible verse, I will be happy to explain why it doesn't conclusively support Eternal Security.
Ephesians 1: 11-14
In him we were also chosen, having been predestined according to the plan of him who works out everything in conformity with the purpose of his will, in order that we, who were the first to put our hope in Christ, might be for the praise of his glory. And you also were included in Christ when you heard the message of truth, the gospel of your salvation. When you believed, you were marked in him with a seal, the promised Holy Spirit, who is a deposit guaranteeing our inheritance until the redemption of those who are God’s possession—to the praise of his glory.
Notice this is taking about predestination, which is another dogma that needs explaining. I'll save that discussion for another time. Suffices to say that Eternal Security and predestination although two different dogmas are related. This, however, does not prove Eternal Security but rather that God has predestined our salvation. It speaks nothing about what will happen if you choose to fall away from God and become an atheist or unbeliever.
For God so loved the world that he gave his one and only Son, that whoever believes in him shall not perish but have eternal life.
I have a lovely source which tackles this Biblical verse. It explains that the problem is tense. The best way to translate the ancient language into modern language and retain the intended tense is thus: For God so loved [past tense] the world that he gave [past tense] his one and only Son, that whoever believes in him [present tense] should not perish [past tense] but has [present tense] eternal life. So if you look at it, it discusses current belief not what you believed in the past. Therefore you have to currently believe in order to be saved. You can't be saved and then become an atheist.
John 10: 28-30
I give them eternal life, and they shall never perish; no one will snatch them out of my hand. My Father, who has given them to me, is greater than all; no one can snatch them out of my Father’s hand. I and the Father are one.”
Several problems. This one talks about no one being able to snatch a believer. It doesn't say anything about the believers free will decision to leave. And, not that I'm a big fan of this but..., John 15 says differently. John 15:6 If you do not remain in me, you are like a branch that is thrown away and withers; such branches are picked up, thrown into the fire and burned. Clearly John 15 says that you need to "remain in me" in order to be saved. Otherwise you loose your salvation. There's a wonderful site that discusses both John 10 and John 15.
Another problem with Eternal Security is that the "once saved, only saved" crowd will say that a person may not have been truly saved. This is confusing to me because I think anyone can truly believe in Jesus but then just as easily fall away from being a follower.
It's a bad analogy, but as children we're taught that Santa Claus is real. We have to behave ourselves all year long and he will come down the chimney, eat cookies, and leave behind presents. We truly believe this because it's what we're taught. We make the cookies, they disappear, presents get left, so we see the evidence as proving the existence of Claus. Yet as we get older, more mature things happen that make us question this belief. We might catch one of our parents eating Santa's cookies or we hear rumors at school that he isn't real. We start asking the hard questions of our parents. Our tiny faith in the jolly ol' man is wavering. Some parents will fluff up the lie by proving that he exists in other ways. Some parents just come out and spill the beans. In the end we discover the truth. The same logic can be applied to one's faith in Jesus. Does that mean a child-like faith isn't definite enough to ensure salvation? I think you can have a child-like faith and be saved. I also think that it's easier to loose faith with a child-like faith. Faith becomes much stronger when it's tested and whatnot. It becomes mature and harder to break.
So the idea that one never had true faith to begin with makes about as much sense to me as saying as a child I could never have believed in Jesus and be saved. Even as young as 2 or 1 when I could speak his name, I believe that I was "saved." Catholics believe that children are saved until they come to the age of reason, which is around age 7, and can make the choice to follow Christ. Now does that make them able to hold a theological debate, not really. Faith for us is a series of wet and dry spells, a journey with the destination being heaven. So we don't really understand how someone can never ever be saved unless it's permanent.
And this is how Eternal Security starts looking more like Predestination, in the Puritanical sense, and not Predestination and Free Will, in the Catholic sense. Free will is the believer actively seeking out and choosing God's grace. Eternal Security seems to squash free will because as I said eternal security says you can only be saved if your faith is permanent. I think, however, I will save that discussion for a later time.
For now I leave you with some other sources of information:
Mark Shea, Catholic news blogger, discusses the dogma and links up Papal Encyclical on topic
Freddie Stewart, Jr., Ignatius Insight, discusses problem with dogma as it divides the relationship with God