This is the final post covering the 'TULIP' acronym that Calvinism is so fond of. The "P" stands for Perseverance of the Saints, and there are various understandings of this so getting an accurate definition is important to see if this is supported by Scripture.
The Westminster Confession of faith defines the "P" thusly: Perseverance of the saints is the Calvinist doctrine that those who are truly saved will persevere to the end and cannot lose their salvation. It doesn’t mean that a person who is truly saved will never lose faith or backslide at any time. But that they will ultimately persevere in faith (in spite of failures) such as not to lose their salvation. The doctrine of perseverance is rooted in God’s unconditional election and predestination. That is, since God is the One who chose and predestined the elect to salvation, therefore the elect will be saved. They might turn away from faith and give appearance of losing their salvation, but if they really are elect they will repent and ultimately return to faith, because God is the One ensuring their salvation.
While not explicitly stated, though strongly implied, this teaches a works-based salvation that one has to persevere in order to be saved. Many Calvinists when pressed on this issue will try and dance around the need (they think) for good works to "stay saved."
Besides the heretical insinuation of "working for salvation" there are several things wrong with this Westminster Confession of Faith. First of all, the fact that a believer cannot lose their salvation is not an exclusively "Calvinist doctrine." This is simply the teaching of Scripture.
The biggest problem with the Westminster Confession above is the method by which our salvation is secure. "Since God is the One who chose and predestined the elect to salvation, therefore the elect will be saved." Obviously, that is totally false and not taught anywhere in the Bible. We covered that in previous posts on the TULIP acronym. It is not because God "predestined us" to be saved that we are saved, but, as John writes in his gospel, "But these are written, that ye might believe that Jesus is the Christ, the Son of God; and that believing ye might have life through his name" (John 20:31).