Therefore, brothers, make every effort to confirm your calling and election, because if you do these things you will never stumble.
For in this way, entry into the eternal kingdom of our Lord and Savior
Jesus Christ will be richly supplied to you.
It is obvious from this passage that the subject matter is important to Peter. He is telling fellow believers to make every effort to confirm (to make sure) of their "calling" and "election". First of all, we need to understand what is meant by those terms, and then to understand why it is so important to be sure of them.
Those particular words have caused much difference of opinion in theological circles for centuries. But, when I have a question, I always go to Strong's Concordance in order to understand what the word was in the original Hebrew or Greek (instead of the sometimes vague or inconclusive English translation). In this case, the word "calling" is from the Greek word, klesis, and the idea of an invitation is being implied. It is used especially of God's invitation to man to accept the benefits of salvation.
The word "election" has all kinds of implications, and is often used to support the theological premise of predestination. When one studies the meaning of its origin in the Greek, one finds that it comes from the word, eklegomai, which means "to pick out, select; to choose for oneself". Interestingly, it does not necessarily imply the rejection of what is not chosen, but "choosing" with the secondary ideas of kindness or favor or love.
And how do we confirm or know that our calling or election are confirmed? Peter says, "If you do these things you will never stumble", thereby affirming your security in them. But what are "these things"? They are the faith, virtue, knowledge, self-control, perseverance, godliness, brotherly kindness, and love that we see evidenced in our lives. (See 2 Peter 1:5-7). As we see these things in our life, we know that our lives are becoming more like the nature of Jesus. It shows that we are being conformed to His image.
As David Guzik points out in his commentary, "It is possible for an unsaved person to do many moral and religious duties. But the "these things" Peter wrote of are matters of the heart, and should be evident in anyone born again. Simply said, if we are called, if we are elect, then we are born again - and if we are born again, it shows in the way that we live". Furthermore, if we continue to grow and progress in our Christian life through these things, it is a sure way to keep from stumbling.
Now, we come to the Why it is important to be sure that we have accepted God's invitation and been chosen to live out a righteous life. It has to do with how you enter into the eternal Kingdom of God. Peter makes it clear that it is important to know where you stand in your Christian walk so that your entry will be "richly" supplied to you. We must not skip over the fact that he makes a point about the state of your entrance. There is more going on here than the knowledge that you will enter the Kingdom of God if you do "these things" and are certain of your "calling" and "election". The object of not stumbling seems to be how you will enter the Kingdom, and Peter is implying that it should be a goal to do it "richly".
The 19th Century British evangelist Frederick Meyer gave a wonderful analogy about our entry into the eternal Kingdom: "There are two ways of entering a port. A ship may come in, waterlogged and crazy, just keeping afloat by continual working at the pumps; or it may enter with every sail set, her flag floating at the mast-head. The latter is what the Apostle Peter desires for himself and those whom he addresses. He desired that an entrance abundant should be ministered unto them."
I'm sure you've heard the contemporary version of this analogy ... something along the lines of "if I can just skid into heaven under the wire, that's good enough for me." But is it? Is that what we really want? Which would you rather accomplish --- to come in unrecognized and unknown, or be welcomed by scores and hundreds or thousands of God's heavenly host to whom you have been the means of a blessing, and who are awaiting you in honor and celebration?
It must not be lost on us that coming into the Kingdom was so important to Peter that he felt it necessary to remind believers to be sure that they did all they could with their invitation from God, so that they could receive the most glorious of entrances. Do you live each day with that in mind? Do we realize that our entrance will be a time of celebration? Which do you want ... to arrive unannounced and unheralded ... or to arrive to the sounds of the heavenly choir singing your praises? We must not take our entrance into eternity for granted, nor as trivial or insignificant. What a glorious day that will be!