What does it mean to "make your call and election sure"?

[KingsGambit]

The entire letter is largely a polemic against false teachers, and perhaps more broadly, warning against apostasy in general. (I don't use this word as an attempt to invoke the Calvinist-Arminian controversy; that has been discussed enough elsewhere). So I see Peter here calling people to seek to be virtuous to make it more difficult for them to fall, and perhaps words it broadly enough so that even people who think themselves secure will pay attention (sort of like what Paul emphasizes in 1 Corinthians 10:12).

[Joel]

The context is:

5 But also for this very reason, giving all diligence, add to your faith virtue, to virtue knowledge, 6 to knowledge self-control, to self-control perseverance, to perseverance godliness, 7 to godliness brotherly kindness, and to brotherly kindness love. 8 For if these things are yours and abound, you will be neither barren nor unfruitful in the knowledge of our Lord Jesus Christ. 9 For he who lacks these things is shortsighted, even to blindness, and has forgotten that he was cleansed from his old sins. 10 Therefore, brethren, be even more diligent to make your call and election sure, for if you do these things you will never stumble; 11 for so an entrance will be supplied to you abundantly into the everlasting kingdom of our Lord and Savior Jesus Christ.

2 Peter 1:5-11 (New King James Version)