"What shall we say then? Are we to continue in sin that grace may abound? By no means! How can we who died to sin still live in it?"
The arguments against "Perseverance of the Saints" should all come to a halt after reading this verse. A true believer cannot and will not continue in sin because Christ lives in Him.
In a real sense, every believer has died. We've been buried in baptism with Christ, and raised up to walk in newness of life. We are no longer the same people we once were: dead, enjoying our trespasses, enemies of God, children of evil, a people of darkness....
Now, a new person has emerged! And this new person hates the things that God hates and loves the things that God loves. Our desires are of those that please God! And more importantly, we hate sin. Many opponents of eternal security make it sound as if a true believer would become lazy and start enjoying sin, thinking that "Well, if I am saved, no matter what I do, I'll still go to heaven." But this is a lie. As Paul says, "Are we to continue in sin that grace may abound? By no means! How can we who died to sin still live in it?"
Show me a man that continues in sin and loves it, and you'll have shown me an unregenerate person. Show me a man who sins, but hates his sin and runs to Christ for His strength, and you'll have shown me a true believer!
1 John 1:6-7
If we say we have fellowship with him while we walk in darkness, we lie and do not practice the truth. But if we walk in the light, as he is in the light, we have fellowship with one another, and the blood of Jesus his Son cleanses us from all sin.
We can have security. And it is lovely to be known by God and to know Him. Once you have become a child of God, adopted into His family by Christ, then you can never, ever be separated from Him. As the days go by, I find myself enjoying God more and more. I am able to run to Him and say, "Abba! Father!" What a gift! What a privilege! What love!