Adam Clarke on 2 Peter 1:8

For if these things be in you and abound - If ye possess all there graces, and they increase and abound in your souls, they will make - show, you to be neither αργους, idle, nor ακαρπους, unfruitful, in the acknowledgment of our Lord Jesus Christ. The common translation is here very unhappy: barren and unfruitful certainly convey the same ideas; but idle or inactive, which is the proper sense of αργους, takes away this tautology, and restores the sense. The graces already mentioned by the apostle are in themselves active principles; he who was possessed of them, and had them abounding in him, could not be inactive; and he who is not inactive in the way of life must be fruitful. I may add, that he who is thus active, and consequently fruitful, will ever be ready at all hazard to acknowledge his Lord and Savior, by whom he has been brought into this state of salvation.