Charles Ellicott Commentary 2 Peter 1:8

"For if these things are yours and abound, they make you to be not idle nor unfruitful unto the knowledge of our Lord Jesus Christ." — 2 Peter 1:8 (ASV)

For if these things be in you.—This is the first reason for the preceding exhortation: the benefit of having these graces. The original Greek meaning of “be in you” is a strong expression, implying permanent and not merely momentary existence.

And abound.—Strictly, and multiply or increase. (Compare to Romans 5:20, and the note there; Romans 6:1; 2 Thessalonians 1:3, where the same inadequate translation occurs in the Authorized Version.)

Neither be barren nor unfruitful.—It is better translated as not idle nor yet unfruitful. Cranmer, Tyndale, and Geneva all have “ydle.” The Greek word literally means “without work”—that is, doing nothing, just as “unfruitful” means producing nothing. The phrase “That you shall be” is not in the Greek and is not needed. The two adjectives “idle” and “unfruitful” exactly correspond to the two verbs “be in you” and “increase.” If these things be in you, you will be morally active; if they increase, you will be morally productive.

In the knowledge.—Rather, it should be unto the knowledge; the fuller, more advanced knowledge mentioned in 2 Peter 1:2–3 and 2 Peter 2:20. This is the goal toward which all these virtues tend, the fruit which they tend to produce—the perfect knowledge of Christ. Those who are most like Christ in their lives have the fullest knowledge of Him in this world, a knowledge to be perfected in the next world when, purified from sin, “we shall see Him as He is.” This clause, without the negatives, accurately describes the condition of the false teachers whom the Apostle has in view.

They were both “idle and unfruitful unto the knowledge of our Lord Jesus Christ.” They neither did nor produced anything that in any degree advanced such knowledge either in themselves or others.

The list of virtues just commended (2 Peter 1:5–7) constitutes a solemn indictment against them. Practical infidelity leading to vicious conduct; a hollow and pretentious philosophy leading to libertinism; an impatience of control leading to utter godlessness; a selfish indifference to the claims of those nearest to them, ending in absolute heartlessness toward all people—such is the charge brought against them, by implication here, and directly in 2 Peter 2.