Perseverance Of The Saints

A doctrine that is much misunderstood & often incorrectly mimicked is the doctrine of the perseverance of the saints.  It is often called the preservation of the saints or sometimes mimicked as "once saved, always saved", "eternal security", or "Lordship salvation".  Perhaps the misunderstanding of this doctrine starts with people who misunderstand who it is doing the persevering.  Being a part of Calvinistic or Reformed doctrine, it should be obvious that it is NOT the individual doing the persevering but that it is God's gracious hand that perseveres.

John 10:28-29

And I give them eternal life, and they shall never perish; neither shall anyone snatch them out of My hand. My Father, who has given them to Me, is greater than all; and no one is able to snatch them out of My Father’s hand.

A usual, & sometimes ridiculing question that is posed by non-Reformed is the question of how a person can claimed to be the "Elect" & yet fall into some error & sin & then at a later time repent & claim that they were the Elect the entire time?  The mocker will often want to claim the person DIDN'T "persevere".  Agan, such a ridicule misunderstands what is meant by this doctrine.
We will start our examination of this doctrine in how it fits into the overall Calvinistic doctrines called the "Five Points" or the T.U.L.I.P. (P = Perseverance of the saints).
The so-called "Five Points of Calvinism" are really a misnomer, since John Calvin himself was dead over 50 years before that term came into parlance.  Though the doctrines articulated by the "Five Points" have always been the mainstay of biblical & historic Christianity, even before the Reformation, it was with the council/synod or canons of Dort in 1618-19 that the doctrine was formally articulated.
To keep our focus, we will not explore the T.U.L. & I of the "tulip" but concentrate primarily on the perseverance.  As stated in the cannons Dort, we better understand what perseverance of the saints really means:

For God, who is rich in mercy, according to his unchangeable purpose of election does not take his Holy Spirit from his own completely, even when they fall grievously. Neither does he let them fall down so far that they forfeit the grace of adoption and the state of justification, or commit the sin which leads to death (the sin against the Holy Spirit), and plunge themselves, entirely forsaken by him, into eternal ruin. (Canons of Dort, Fifth Main Point, Article 6)

Further, we can see that this perseverance is the evidence that it is God actually sustaining the Elect.

So it is not by their own merits or strength but by God's undeserved mercy that they neither forfeit faith and grace totally nor remain in their downfalls to the end and are lost. With respect to themselves this not only easily could happen, but also undoubtedly would happen; but with respect to God it cannot possibly happen, since his plan cannot be changed, his promise cannot fail, the calling according to his purpose cannot be revoked, the merit of Christ as well as his interceding and preserving cannot be nullified, and the sealing of the Holy Spirit can neither be invalidated nor wiped out. (Canons of Dort, Fifth Main Point, Article 8)

Thus, those who ridicule Christians who may for a time fall prey to sin or error are altogether uninformed of the doctrine of the perseverance of the saints.
Scripture articulates this doctrine many places but perhaps one of the best places is in Philippians 1:6

being confident of this very thing, that He who has begun a good work in you will complete it until the day of Jesus Christ

All of this does NOT negate man's responsibility to live a holy life, as a reflection of Christ that is within us.