Jamieson, Fausset and Brown on 2 Peter 1:15

15. endeavour--"use my diligence": the same Greek word as in 2Pe 1:10: this is the field in which my diligence has scope. Peter thus fulfils Christ's charge, "Feed My sheep" (Joh 21:16, 17).

decease--"departure." The very word ("exodus") used in the Transfiguration, Moses and Elias conversing about Christ's decease (found nowhere else in the New Testament, but He 11:22, "the departing of Israel" out of Egypt, to which the saints' deliverance from the present bondage of corruption answers). "Tabernacle" is another term found here as well as there (Lu 9:31, 33): an undesigned coincidence confirming Peter's authorship of this Epistle.

that ye may be able--by the help of this written Epistle; and perhaps also of Mark's Gospel, which Peter superintended.

always--Greek, "on each occasion": as often as occasion may require.

to have ... in remembrance--Greek, "to exercise remembrance of." Not merely "to remember," as sometimes we do, things we care not about; but "have them in (earnest) remembrance," as momentous and precious truths.