This verse together with verse 9 explains the importance of possessing the virtues just mentioned. Verse 8 describes the benefits for people who possess these virtues, while verse 9 describes the negative condition of people who lack these virtues.
If these things are yours and abound: this stresses two things. In the first place these virtues must truly be possessed and fully at a person’s disposal; and secondly, these virtues must continue to be developed in a person’s life. Other ways of translating this clause are: “You need to have these qualities, and if you have them in a great measure…,” or idiomatically, “You need to … and if they grow strong in your heart….”
The result of possessing and fostering these virtues is stated negatively: it keeps the believers from being ineffective or unfruitful in the knowledge of our Lord Jesus Christ. They keep you is a causal construction; in some languages it may be expressed as “they will cause you to.” The words for ineffective and unfruitful are very similar in meaning and stress the importance of good actions in the Christian life. It must be noted that both of these words are negatives that sometimes can be translated positively. Thus ineffective can also be “useless” (New English Bible), “complacent” (Phillips), or positively, “active” (Good News Translation), “to have ability.” Unfruitful can also be “barren” (New English Bible), “unproductive” (Phillips), or positively, “effective” (Good News Translation), “successful,” “useful.” Hence this whole negative construction can also be expressed positively, as in Good News Translation “they will make you active and effective in your knowledge of our Lord Jesus Christ.”
How are these virtues related to the knowledge of our Lord Jesus Christ? First of all, knowledge of Christ may be viewed as the goal of the virtuous life; a life of virtue leads to a fuller and more effective knowledge of Jesus Christ (see Jerusalem Bible “they will not leave you ineffectual or unproductive: they will bring you to a real knowledge of our Lord Jesus Christ”). But secondly, however, the Greek preposition for in can be taken with the meaning “with reference to” or “in respect to.” If the preposition is taken in this manner, the knowledge of Christ becomes the root of the virtuous life; the lives of believers are determined by their knowledge of Christ.
An alternative translation model for this verse is the following:
These are the qualities you need, and if you really know our Lord Jesus Christ, you will have them strong in your heart. This will produce good results in your life.
Quoted with permission from Arichea, Daniel C. and Nida, Eugene A. A Handbook on The Second Letter from Peter. (UBS Handbook Series). New York: UBS, 1980. For this and other handbooks for translators see here .