Eternal Security is true...If it is not separated from the conditions of salvation. Otherwise Eternal Security is false. No one who has ever made a profession of faith has any reason to believe that they will finally be saved if they do not continue believing and repenting. Likewise the 'believer' who does not repent has no reason to believe that they are Eternally Secure. On the flip side of this, no 'repenter' who does not believe has any reason to think that they will be saved.
Let me explain further.
Those who claim to trust Christ and yet continue living in their sin and do not experience sanctification are not truly trusting Christ. They do not have Biblical faith.
But we ought always to give thanks to God for you, brothers beloved by the Lord, because God chose you as the firstfruits to be saved, through sanctification by the Spirit and belief in the truth. To this he called you through our gospel, so that you may obtain the glory of our Lord Jesus Christ. So then, brothers, stand firm and hold to the traditions that you were taught by us, either by our spoken word or by our letter. Now may our Lord Jesus Christ himself, and God our Father, who loved us and gave us eternal comfort and good hope through grace, comfort your hearts and establish them in every good work and word. (2Th 2:13-17)
Five basic truths are revealed in these verses. First, God chose us to salvation. Second, salvation is through sanctification. Third, salvation is through belief in the truth. Fourth, we are called to salvation through the Gospel. Fifth, salvation is equated to obtaining to the glory of our Lord Jesus Christ.
Points two and three are the relevant points in this study. These verses clearly state that without sanctification, there is no salvation. They also state that without faith (belief in the truth), there is no salvation.
This is only one text but these points are clearly demonstrated elsewhere through Scripture.
Mark 1:14-15 are interesting verses.
Now after John was arrested, Jesus came into Galilee, proclaiming the gospel of God, and saying, "The time is fulfilled, and the kingdom of God is at hand; repent and believe in the gospel." (Mar 1:14-15)
Jesus preached that in order to be saved that we must believe and repent.
But back to our original text. Where belief in the truth is not present (faith), salvation is not present. Where sanctification is not present, neither is salvation.
We have labored the point on Biblical faith elsewhere, so now we want to look at sanctification.
Sanctification is being set apart for service. It denotes a consecration. It is the act of God separating us to Himself and His service.
Sanctification is also a growing in purity. This is where repentance comes in. Repentance is turning from sin to Christ. Sanctification is cleansing ourselves by the power of the Spirit, and becoming more like Christ. It is also, according to our text, a means of salvation. We are being saved 'through sanctification by the Spirit.'
This is why Calvinists typically do not use the term Eternal Security. Eternal Security, as taught in its most popular form says that after a one time confessing of Jesus as Lord, and a one time repenting of our sins, and a one time belief in the truth, we are secure. In its true form it is taught that those who truly believe cannot lose their salvation.
Calvinists prefer the term Perseverance of the Saints. This term includes Eternal Security and adds that those who are truly saved and have truly believed will continue believing and repenting and growing in sanctification until death or the return of Christ. They will never fall away from Christ and their not falling away is characterized by a sanctified and holy life. They have been eternally saved, are being saved, and will finally be saved as they persevere to the end.
Thank you for persevering to the end of my ramblings on what Calvinism is and is not.