The ‘if’ in the text CANNOT possibly mean that the brethren will lose their salvation ‘if ‘they forget in their brain what Paul preached to them. That being the case then a saved person who has a brain disorder such as Alzheimer’s disease and they do not have in memory the Gospel which Paul declared, then according to the ‘conditional’ security experts the text says the person is lost.
Paul addresses the church of Corinth, as there has obviously been some misunderstanding about the Gospel of grace which Paul had been teaching. (1 Corinthians 15:12 Now if Christ be preached that he rose from the dead, how say some among you that there is no resurrection of the dead?) Paul wants to clear this up as he is a faithful witness of Christ (1 Corinthians 15:15 Yea, and we are found false witnesses of God; because we have testified of God that he raised up Christ: whom he raised not up, if so be that the dead rise not.) Remember Paul had taught the Corinthians by preaching the word ( vrs 12) so in verse 2 he says ‘if ye keep in memory what I preached’ is the same as what I’m about to write in verses 3 & 4. In other words, if you are teaching that there is no risen Saviour then you are still in your sins because you’ve misunderstood my preaching and you were never saved in the first place.
Hence the ‘brethren’ are Corinthians who received the gospel, stand in the gospel, and are saved by believing the gospel written in verses 1 Cor: 3 & 4 according to the scriptures. Also, these first two verses are also aimed at the unsaved Corinthians who are thought to be ‘brethren’ and are part of the church set up, but they believe in a dead Saviour Jesus Christ, so their faith is vain and they are still lost because they never believed according to the scriptures ( vrs 2, 14 And if Christ be not risen, then is our preaching vain, and your faith is also vain., 17 And if Christ be not raised, your faith is vain; ye are yet in your sins.,) Paul tells the Corinthians that the so called ‘brethren’ in the church who are telling everyone “that there is no resurrection of the dead” that they were never saved in the first place because their belief was in vain.
Please notice the comma after the word ‘saved’ which separates ‘saved’ and ‘if ’. At this time the comma indicates that Paul switches the brethren to their memory of the events of their own salvation when he preached and says that what he is about to write ( vrs 3 & 4) shouldn’t be strange or alien to them ( in memory ) unless they have believed in vain.
Believing the word of God, and allowing the scriptures to speak for themselves, gives the answer to the insecurists, that their pet doctrine IS another gospel ( Gal 1:8). Verse 2 definitely doesn’t mean that there was a condition to keep them saved, but it does say that there is a condition in getting saved. That condition is to believe the gospel according to the scriptures ( vrs 3 & 4 ).
So according to sound doctrine Paul’s Gospel is NOT Conditional as far as keeping salvation! (Taken from Conditional Security refuted by Kevin Rae)