"For I am persuaded that neither death nor life, nor angels nor principalities nor powers, nor things present nor things to come, nor height nor depth, nor any other created thing, shall be able to separate us from the love of God which is in Christ Jesus our Lord." - Romans 8:38-39
These words provide great comfort, reminding us that we are secure in God's love, not because of who we are, but because of who He is. No created thing can separate us from God's love, and you, my friend, are a created thing.
But this comfort can easily be erased. If you are so inclined, you may fall for the lies of any number of works-based "gospel", which tell us there is one exception to this rule. Though nothing can separate us from the love of God, you can separate yourself from it through sin.
Of course, there is some truth to this. Sin and God do not mix. For this reason, each and every one of us began as enemies of God. We were under His curse, and it took Jesus' death to set us free from this burden. Furthermore, those who never come to faith in Christ retain this sentence of death. By rejecting God's love, they forfeit the privilege.
But the difference between saint and sinner is not the sin itself. In fact, John warns us that to believe it is makes us a part of the latter category: "If we say that we have no sin, we deceive ourselves, and the truth is not in us. If we confess our sins, He is faithful and just to forgive us our sins and to cleanse us from all unrighteousness. If we say that we have not sinned, we make Him a liar, and His word is not in us." (1 John 1:8-10).
From this, we see that if sin was enough to separate us from God's love, all of us would be separate from God's love. But this is not the case, for John continues "My little children, these things I write to you, so that you may not sin. And if anyone sins, we have an Advocate with the Father, Jesus Christ the righteous. And He Himself is the propitiation for our sins, and not for ours only but also for the whole world." (1 John 2:1-2).
We see, then, that rather than sin separating us from the love of God, Christ advocates on our behalf. But we don't actually need to go to John to see this, for Paul himself, in the same chapter, tells us "What then shall we say to these things? If God is for us, who can be against us? He who did not spare His own Son, but delivered Him up for us all, how shall He not with Him also freely give us all things? Who shall bring a charge against God’s elect? It is God who justifies. Who is he who condemns? It is Christ who died, and furthermore is also risen, who is even at the right hand of God, who also makes intercession for us. Who shall separate us from the love of Christ? Shall tribulation, or distress, or persecution, or famine, or nakedness, or peril, or sword? As it is written: “For Your sake we are killed all day long; We are accounted as sheep for the slaughter.” Yet in all these things we are more than conquerors through Him who loved us." (Romans 8:31-37).
We see, then, that those who read verses 38-39 and confidently assert "but you can forfeit it through sin" are actually sinning themselves by twisting the word of God. Context is king, and in this case, the immediate context directly and explicitly refutes the objection. Sin cannot separate you from the love of God! In fact, Paul also says "But God demonstrates His own love toward us, in that while we were still sinners, Christ died for us." (Romans 5:8).
Of course, this is where Conditional Security advocates miss the point completely and ask "then why not just continue to sin?" "What shall we say then? Shall we continue in sin that grace may abound? Certainly not! How shall we who died to sin live any longer in it? Or do you not know that as many of us as were baptized into Christ Jesus were baptized into His death? Therefore we were buried with Him through baptism into death, that just as Christ was raised from the dead by the glory of the Father, even so we also should walk in newness of life." (Romans 6:1-4).
The fact that I had a Scripture locked and loaded, ready to answer that objection, is not simply a matter of convenience. Rather, it is a natural result of God's genius. He knew not only that some would doubt Him, and therefore raise this objection against His Gospel, but also that there would absolutely be Christians who would take His grace and run with it in this exact manner. Why? Well, because it's just human nature. If we know what we can get away with, the chances are higher we'll try to get away with it. But God's simple answer can be summed up in this memorable phrase: Grace is a safety net, not a hammock.
But note something else here. Does Conditional Security merit the objection "we should continue to sin that grace may abound"? Of course not! Those who believe in Conditional Security will always have one of two attitudes: Pride, or fear.
They may be proud, either because they believe they are without sin, or because they believe their sins are "small". To that, James says that to offend one time is to be guilty of all (James 2:10). Thus, no, your sin is not small. If He judges us by our works, all of us are going to Hell. The flip side is fear, believing they are, or at the very least might be, too sinful to be saved.
Neither of those attitudes are going to lead to "great! Let's continue to sin that grace may abound!" Rather, they'll lead to "I'm not going near sin, lest I lose my salvation." Thus, the objection Paul anticipates, "Shall we continue in sin that grace may abound?", makes sense. His response, however, only makes sense if He is genuinely preaching Eternal Security. He's effectively telling us there is another reason not to go on sinning. It's not because otherwise, you will lose your salvation, but rather, it is because you have been saved!
So, can sin separate us from the love of God? Absolutely not. You are among the created things that cannot separate you from the love of God. This is why we should not sin, but if you sin, Christ, because of His love, continues to advocate for you. Therefore, you should make every sin your last, but you should not fear that Christ will make every intercession His last.