Closing his letter, Part II

Guarding our hearts . . .  Here's our passage again:

You therefore, beloved, since you know this beforehand, beware lest you also fall from your own steadfastness, being led away with the error of the wicked; 18 but grow in the grace and knowledge of our Lord and Savior Jesus Christ. To Him be the glory both now and forever. Amen. (II Peter 3:17-18, NKJV)

And for comparison, here it is in another translation:

Therefore, dear friends, since you have been forewarned, be on your guard so that you may not be carried away by the error of the lawless and fall from your secure position. 18 But grow in the grace and knowledge of our Lord and Savior Jesus Christ. To him be glory both now and forever! Amen. (II Peter 3:17-18, NIV)

It's always interesting to me to compare the different translations. Without going down too many rabbit trails, I do believe that some translations are more accurate than others, and that comparing many of them will enable the Spirit to guide us as to what the ancient writers were trying to say to us. Some people have gotten "hung up" on that last phrase of verse seventeen, and have tried to say that it's telling us we can lose our salvation.
No!
It's telling us that we can fall away from our secure, steadfast confidence that keeps us knowing we are children of God and loved by Him. It means that we can lose our peace, our "we know that we know" confidence in the Lord. All by being swept up by false teachers.
We must guard our hearts from spiritual errors.
There are several references in the New Testament to false teachers who will come into the body of believers -- they sound biblical, but they lead Christians away from the truth. Peter, himself, has warned us in chapters two and three about these teachers.
The noun used here for "steadfastness" is only used here. Perhaps Peter wanted to show his concern, with his own personal history of wavering and denying Christ. He is encouraging us to grow by God's grace into rock-like steadfastness, just as he did.

Recently we studied Peter's previous words, telling of unstable, unprincipled, lawless people who will twist Scripture to support their immoral lifestyles. We must be on our guard against these. They will use the Bible, but they will cite things out of context. Or they will only use certain verses that support their point of view, all the while ignoring verses that confront their sin. And we must not fall into the well-look-how-big-that-church-is-the-preacher-must-be-good-and-true trap . . . some of the largest churches in the world today are led by men and women who mix truth and error in subtle ways.
How to test them?
Probably the best rule of thumb is this: if a speaker never confronts sin, they are not preaching the Word of God.

In the presence of God and of Christ Jesus, who will judge the living and the dead, and in view of his appearing and his kingdom, I give you this charge: 2 Preach the word; be prepared in season and out of season; correct, rebuke and encourage—with great patience and careful instruction.  (II Timothy 4:1-2)

After all, the Bible has some teachings that confront the popular ideas of our cultures today. Let's face it: people want to hear that there is good in all of us. That we are shaped by our environment, and not to blame for our choices.
It's not popular to say that we are all born in sin. That we are hopelessly lost, and we're unable and unwilling to come to Christ for salvation. It's more flattering to our prideful hearts to say that we're not really so bad - we just mess up once in a while - we don't really deserve hell.

And it's not popular to say that Jesus is the only way to heaven; that those from other religions (no matter how sincere) will not go to heaven unless they turn from their sins and trust in Jesus alone.

It's not at all popular to teach that we must submit our lives to Christ as our Lord and our Master. It's way more palatable for people to hear that grace means that God winks at our sin. And that Jesus is there to help us reach our full potential and our material goals. We may be accused of being legalistic and devoid of understanding because we say we must obey our Savior.

It's not only unpopular, it may soon be criminal to teach that homosexual behavior and sex outside of marriage is sinful. The list could go on and on, but I think you get my drift here.

We've probably been told that it's not loving to be critical and firm about these matters. We're told that we should be positive and not negative. But remember that Peter has addressed his readers as "beloved" and "dear friends." He cares deeply for these Christians and so he is warning them to guard their hearts against false teachers. Because we love our children, we warn them sternly about leaving the sidewalk and stepping into the street. Because we love our children and our friends, we warn them about the dangers of drugs, drinking, and more. These are choices that can have serious consequences, and permanent scars. Love is not merely positive; it has a negative side, and that is warning others about sin and false teaching.

One last application here: there is a link between our knowledge and our behavior. We must prepare to guard our hearts by careful study of the Bible, and also books on basic Christian doctrines. A short list would include these and others: A Faith to Confess, Carey Publications; Dug Down Deep, Josh Harris; Essential Truths of the Christian Faith, R. C. Spruel.
To persevere as a believer, we must guard ourselves from spiritual error, and exhort others to guard themselves, too.