You will be neither barren nor unfruitful in the knowledge of our Lord Jesus Christ

2 Peter 1:8
For if these things are yours and abound, you will be neither barren nor unfruitful in the knowledge of our Lord Jesus Christ.

This verse continues from talking about fruits (faith, virtue, knowledge, self-control, perseverance, godliness, brotherly kindness, love) that are developed once we are in the Lord. So when we have developed each of the virtues, we become aware of them. Of course the virtues itself does not always mean we are productive in the Kingdom. However they do indicate we become more and more equipped to serve in the Kingdom.