Why do I have a picture of a tent here? Read on...
12 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. 13 Yes, I think it is right, as long as I am in this tent, to stir you up by reminding you, 14 knowing that shortly I must put off my tent, just as our Lord Jesus Christ showed me. 15 Moreover I will be careful to ensure that you always have a reminder of these things after my decease. 16 For we did not follow cunningly devised fables when we made known to you the power and coming of our Lord Jesus Christ, but were eyewitnesses of His majesty. 17 For He received from God the Father honor and glory when such a voice came to Him from the Excellent Glory: “This is My beloved Son, in whom I am well pleased.” 18 And we heard this voice which came from heaven when we were with Him on the holy mountain.
“For this reason,” i.e. because of the need for Christians to grow in virtue and in personal knowledge of God, St. Peter has reminded them of their need, even though they already know it. There are some things in our Christian lives that we can never hear too many times. For example, even though all Christians know that it is important to pray, we forget, we get lazy, we grow discouraged, and so on. Because of this, we need to read and hear about the importance of prayer over and over again. The same is true for many other things. Examples include the need to show love to others, the need to be humble, the need to give generously to God, the need to be regular in attending divine services, and the need to regularly read the Scriptures (among others). We must, to use St. Peter’s language, constantly be “stirred up” (and also to “stir up” others who need encouragement).
Another reason St. Peter gives for reminding his audience of the basics of the faith is because he knows that his death is imminent. The great Neronian persecution of the Church that followed the great fire in Rome had just begun, and St. Peter knows that it is just a matter of time before he and all the other leaders of the Church would be rounded up and put to death. And not only this, but Christ had personally shown him in some way. Using a picturesque metaphor, the apostle says that he is about to “put off my tent.” Because he must soon leave the earth, St. Peter wants his readers to “always have a reminder of these things after my decease.”
He then goes on to assure them that the Gospel that he and the other Apostles had preached was not a set of “cunningly devised fables” like the Greek and Roman mythologies or the Gnostic teachings. Instead, they were telling what they had seen and heard (compare 1 John 1:1) in the years that they had spent with Christ. For St. Peter and the other apostles were “eyewitnesses of His majesty.” This “majesty” is almost certainly a reference to the Transfiguration of Christ, for then not only did St. Peter see Christ’s majesty and glory, but they also heard the voice of the Father saying “This is my beloved Son, in whom I am well pleased.”
FF comments thus: “This, Peter says, proves the reality of the Second Coming, for Christ Himself pointed to the Transfiguration as a foretaste and proof of His future glory at the Coming (Matt. 16:28). The greatness He will manifest at the Second Coming was observed by the apostles at His Transfiguration. The apostles thus can confidently proclaim the reality of His Coming because they themselves have seen its glory already” (120).