On Tuesday I wrote how some criminals take advantage of God's forgiveness and use it as a license to sin (something Paul says is a big no-no in Romans 6:1-4). I also partly blamed this on bad theology that teaches that once God has legally declared we are justified we stand no chance of going to hell. This view is also called "Once saved, always saved."
In the previous post I showed that this idea doesn't make logical sense because it would lead to the conclusion that believers who fall away from the faith at a later time were never "saved" to begin with.
Now I'd like to examine two scripture passages that are used to support the view that a Christian can never lose his salvation (or eternal security).
Philippians 1:6: I am confident of this, that the one who began a good work in you will continue to complete it until the day of Christ Jesus.
Paul is praising the Philippians in particular, not all Christians, when he expresses his confidence. The Philippian Church was the only one generous enough to support him in his time of struggle (Phil. 4:14-16). In 2:12 we also read of their obedience, which was the source of Paul’s confidence in them. Regardless, in the same verse where Paul describes their obedience (2:12) he still tells them to “work out their salvation in fear and trembling.”
1 John 5:13: I write these things to you so that you may know that you have eternal life, you who believe in the name of the Son of God.
Earlier in the letter, the author of 1 John describes essential attributes one must have in order to be a true believer in the son of God. In 3:10 he says, “No one who fails to act in righteousness belongs to God, nor anyone who does not love his brother.” In 5:3 he says, "For the love of God is this, that we keep his commandments. And his commandments are not burdensome.” If we believe in the son of God we will keep his commandments, but if we do not keep the commandments, then we do not believe in him and can’t know that we are saved.
For a longer treatment of this subject see the Catholic Answer's tract Assurance of Salvation?