2 Peter 1:8

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

And abound. — Strictly, and multiply or increase. (Comp. Romans 5:20, and Note there; Romans 6:1; 2 Thessalonians 1:3, where the same inadequate translation occurs in the Authorised version.)

Neither be barren nor unfruitful. — Better, not idle nor yet unfruitful. Cranmer, Tyndale, and Geneva all have “ydle.” The Greek word literally means “without work” — i.e., doing nothing, as” unfruitful” means producing nothing. “That ye 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, unto the knowledge; the fuller, more advanced knowledge of 2 Peter 1:2, and 2 Peter 2:20. This is the goal towards which all these virtues tend, the fruit which they tend to produce — the perfect knowledge of Christ. Those who are the 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) 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 towards all men — such is the charge brought against them, by implication here, directly in 2 Peter 2.