1:16-19 How are we to understand what Peter says here?

Here Peter refers to the second coming of Jesus, which was foreshadowed by His transfiguration on the mount to which Peter himself, together with James and John, was an eyewitness (CP Lu 9:28-36 (also Mt 17:1-8 and Mk 9:1-8); Jn 1:14).

In 2Pe 1:16-19 Peter compares his experience at Jesus' transfiguration to the abiding, prophetic word of scripture. He teaches that the testimony of scripture is a surer confirmation of God's truth concerning Jesus than even the supernatural events of the transfiguration.

Peter is not detracting from the events of the transfiguration but he wants believers to see that not even supernatural experiences such as the transfiguration, holds greater authority than the established word of God. The word contains everything we need - for salvation, for faith, for obedient living (CP Psa 19:7; 119:9, 101-105, 130; Pr 6:23; 30:5; Jn 17:3-17).

Peter likens the word to a lamp that lights up a dark, squalid place, and he admonishes believers to feed upon it until the light of the word dawns in their soul, and Christ, who is the morning star, shines in their heart (CP Rev 2:28; 22:16).

The idea behind what Peter says in 2 Pe 1:16-19 is for believers to flood their entire inner man with the radiating light of Christ and the revelation of the word until His return (CP Jn 1:4-5, 9; 2Cor 4:5-7).

When the day dawns in 2Pe 1:19, refers to Christ's second coming, when the revelation of Christ in our hearts will be complete (CP 1Cor 13:12; 2Cor 3:18; 1Jn 3:2). See also comments on Mt 16:28. 1:20-21

Is this teaching as some claim that only those holding high office in the church have the authority to interpret scripture?

No, Peter is simply teaching here that the words of scripture are not what the prophets thought up for themselves, but that they were given to them to write by the Holy Spirit. It is because the scriptures are divinely inspired that they must be heeded (CP V 19 with Psa 119:9; Ro 15:4; 2 Ti 3:16-17).

2 Peter