2 Peter 3:1-2

3 This is now, beloved, the second letter I am writing to you in which I am stirring up your sincere mind by way of reminder, 2 that you should remember the words spoken beforehand by the holy prophets and the commandment of the Lord and Savior spoken by your apostles.

These verses may serve as an introduction to the teaching that is coming next: on the last days. Peter calls them to remember what the Old Testament prophets said about the last days, and also what “the commandment of the Lord and Savior spoken by your apostles” says about the last days. This last term (which I have here in quotes) is the revealed word of God that was spoken by the apostles.