For those who believe in the doctrine of eternal security, II Peter 1:10-11 is a particularly difficult passage to dispute because it exposes the lie in this infernal teaching. It does this by stating a simple command that God asks us to carry out.
The inverse is also true; if we fail to do what Peter advises, then our calling and election are not sure. Beyond that, if we stumble, an entrance will not be supplied to us into the Kingdom of God.
God has done His part. He called or elected us out of all the billions on this planet. He forgave us, granted us repentance, and gave us His Holy Spirit. He opened up the truth to us and revealed Himself and His way of life to us. He made the New Covenant with us, supplying us with spiritual gifts, love, and faith. There is no end to what He has done for us.
Nevertheless, if we do not reciprocate, the relationship He has begun will fall apart. Our calling and election are not certain without us doing our part. We can fall away and not make it into the Kingdom of God.
Why did Peter write this to the whole church (verse 1)? He wrote it because the church at the time was experiencing various apostasies (II Peter 2:3). False teachers were bringing into the church destructive doctrines to turn the people away.
Why would Satan put false teachers in the church if there was no chance for the people to fall away? If church members have eternal security, why waste his time on them? However, Satan himself knows that Christians do not have eternal security, and he tries his best to turn us into apostates. We can fall away!
Peter was writing in this atmosphere. The people in the first-century church were living in a time of false teachings, false teachers, and apostasy, and he needed to warn them. "For this reason I will not be negligent to remind you always of these things, though you know and are established in the present truth" (II Peter 1:12).
This, too, begs the question: Why did Peter command them to make their calling and election sure? If they had the truth, and he admitted that they were established in it, why did they have to make it "sure"? In making their calling and election sure, they would be doing the one thing that would keep them on the right path to the Kingdom. Christians keep themselves from falling into deception, error, and sin - keep themselves from apostatizing and losing their salvation - by validating their conversion.
When a thing is validated, it is objectively determined to be genuine, true, real, authentic, or legitimate. How do Christians validate their calling and election? The answer is simple. Jesus describes it in Matthew 7:16-20: We validate our calling and election by producing fruit. Jesus expounds on this in His Passover message in John 15:
I am the true vine, and My Father is the vinedresser. Every branch in Me that does not bear fruit He takes away. And every branch that bears fruit He prunes, that it may bear more fruit. . . . As the branch cannot bear fruit of itself, unless it abides in the vine, neither can you, unless you abide in Me. I am the vine, you are the branches. He who abides in Me, and I in him, bears much fruit; for without Me you can do nothing. If anyone does not abide in Me, he is cast out as a branch and is withered. And they gather them and throw them into the fire, and they are burned. . . . By this My Father is glorified, that you bear much fruit; so you will be My disciples. (verses 1-2, 4-6, 8)
This blows the eternal security doctrine to smithereens. Our Savior, Jesus Christ - our Judge - says that if we do not bear fruit, God will take us away and throw us into the fire! If we bear fruit, however, we will glorify the Father and truly be disciples of Christ, that is, true Christians!
We validate our calling by growing in grace and knowledge (II Peter 3:18). If we are showing love to the brethren, if we are serving as opportunity permits, if we are deepening our relationship with God, we can be certain that our calling and election are still firmly in force.