2 Peter 1:20 Knowing this first, that no prophecy of the scripture is of any private interpretation. 21 For the prophecy came not in old time by the will of man: but holy men of God spake as they were moved by the Holy Ghost. The indwelling of the Holy Spirit. Not the private interpretation of man.
You didnt finish the passage again. He say that those who know what to watch for. He said in verse 16 that those who have a hard time understanding are unlearned and unstable. Then in verse 17 he warns not to get caught up in what the unlearned say.
2 Peter 3:17 Ye therefore, beloved, seeing ye know these things before, beware lest ye also, being led away with the error of the wicked, fall from your own stedfastness. 18 But grow in grace, and in the knowledge of our Lord and Saviour Jesus Christ. To him be glory both now and for ever. Amen.
He says if we listen to those who are unlearned and unstable we will fall from our own stedfastness. We must have been in a state of learned and steadfastness for us to fall from it right? Which would mean that we already understand and dont find it hard to understand.