A.T. Robertson 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 are yours and abound (ταυτα γαρ υμιν υπαρχοντα κα πλεοναζοντα). Present active circumstantial (conditional) participles neuter plural of υπαρχω and πλεοναζω (see 1 Thessalonians 3:12) with dative case υμιν, "these things existing for you (or in you) and abounding."

They make you to be (καθιστησιν). "Render" (present active indicative of καθιστημ, old verb, James 3:6), singular because ταυτα neuter plural.

Not idle nor unfruitful (ουκ αργους ουδε ακαρπους). Accusative predicative plural with υμας understood, both adjectives with alpha privative, for αργος see Jas 2:20 and for ακαρποςMatthew 13:22.

Knowledge (επιγνωσιν). "Full (additional) knowledge" as in 1:2.