A.T. Robertson Commentary John 15:16

"Ye did not choose me, but I chose you, and appointed you, that ye should go and bear fruit, and [that] your fruit should abide: that whatsoever ye shall ask of the Father in my name, he may give it you." — John 15:16 (ASV)

But I chose you (αλλ' εγω εξελεξαμην υμας). First aorist middle indicative of εκλεγω. See this same verb and tense used for the choice of the disciples by Christ (6:70; 13:18; 15:19). Jesus recognizes his own responsibility in the choice after a night of prayer (Luke 6:13). So Paul was "a vessel of choice" (σκευος εκλογης, Acts 9:15). Appointed (εθηκα). First aorist active indicative (κ aorist) of τιθημ. Note three present active subjunctives with ινα (purpose clause) to emphasize continuance (υπαγητε, keep on going, φερητε, keep on bearing fruit, μενη, keep on abiding), not a mere spurt, but permanent growth and fruit-bearing.

He may give (δω). Second aorist active subjunctive of διδωμ with ινα (purpose clause). Cf. 14:13 for the same purpose and promise, but with ποιησω (I shall do). See also 16:23f.,26.