He goes on to say that in order to shy away from spiritual ignorance, thus living in the divine nature [2 Peter chapter one] his readers - as well as you and I - must 'grow in the grace and knowledge of...Christ.'
Why? And how does this relate to being a productive teacher. Not only a productive teacher, but one that's able to brush off and defeat false teachings that exploit and destroy without understanding or care[chapter two].
Peter wrote these passionate instructions around the same time that his cohort Paul, while in prison, wrote his second very personal letter to his favorite son - Timothy. I realize how absurd it is to ask 'why' it's important to continue growing in Christ, it's obvious right? Tell me this, how much do you study the life of the Messiah. If you're fully matured in Christ-likeness then by all means, don't waste your time. Otherwise, it's not such an absurd question and reminder is it? Though the answer can be found throughout the entire body of Scripture, Paul sums it up a bit while encouraging Tim, he says that all Scripture (even the new stuff) is God-breathed - Theopneustos: the very breath/wind/spirit of YHVH infused into the logos, the word - and used for teaching, rebuking, correcting and training up in the righteousness of God [2 Timothy chapter three].
Growing in Christ, according to Peter and Paul, equips us to graciously serve with the wisdom of God. Teaching is an obese part of that service, very weighty responsibility. As the student learns from the Teacher he is equipped to continue the spiritual tradition of passing on the Word, in truth.
So grow, breathe in the attitude of Christ.