A.T. Robertson Commentary John 15:19

"If ye were of the world, the world would love its own: but because ye are not of the world, but I chose you out of the world, therefore the world hateth you." — John 15:19 (ASV)

The world would love its own (ο κοσμος αν το ιδιον εφιλε). Conclusion of secondclass condition (determined as unfulfilled), regular idiom with αν and imperfect indicative in present time.

But because ye are not of the world (οτ δε εκ του κοσμου ουκ εστε). Definite and specific reason for the world's hatred of real Christians whose very existence is a reproach to the sinful world. Cf. 7:7; 17:14; 1 John 3:13. Does the world hate us? If not, why not? Has the world become more Christian or Christians more worldly?