Growth in grace is an increase in the experience of the benefits of salvation (1 Peter 1:10; 1 Peter 3:7; 1 Peter 4:10; 1 Peter 5:5, 1 Peter 5:12) or growth in favour with God (1 Peter 2:19–20).1 Knowledge probably refers to knowledge of Christ or more specifically knowledge that Peter has shared in his letter. With the final verse of the letter serving as an inclusio with 2 Peter 1:2 (see how they both refer to grace and knowledge), this would suggest that the knowledge in which believers must grow is that which is contained in the body of the letter (2 Peter 1:3 – 3:18a).
18 But grow in the grace and knowledge of our Lord and Savior Jesus Christ. To him be the glory both now and to the day of eternity. Amen.