This book is written to believers Elsie
Piper says it this way
Peter is saying "Confirm your election! Make sure of it!" How? By standing in your faith and pressing on to virtue, knowledge, self-control, patience, godliness, brotherly affection and love. John said (in 1 John 3:14), "We know that we have passed out of death into life, because we love the brethren" (cf. 2:3). The confirmation of your election is your progress in sanctification. God predestined all the elect to be conformed to the image of Christ (Rom. 8:29). Therefore, the reassuring evidence of our election is Christ-likeness.
I say it is all of God..from begining to end ..His grace called me,saved me and preserves me. He is the author and finisher of my faith ..not one wit me
Phl 2:13 For it is God which worketh in you both to will and to do of [his] good pleasure.
WHY does it need to be confirmed?
WHY does it need to be reassured?