Jamieson, Fausset and Brown on Philippians 1:11

11. The oldest manuscripts read the singular, "fruit." So Ga 5:22 (see on Ga 5:22); regarding the works of righteousness, however manifold, as one harmonious whole, "the fruit of the Spirit" (Ep 5:9) Jas 3:18, "the fruit of righteousness" (He 12:11); Ro 6:22, "fruit unto holiness."

which are--"which is by (Greek, 'through') Jesus Christ." Through His sending to us the Spirit from the Father. "We are wild and useless olive trees till we are grafted into Christ, who, by His living root, makes us fruit-bearing branches" [Calvin].