A.T. Robertson Commentary John 15:25

"But [this cometh to pass], that the word may be fulfilled that is written in their law, They hated me without a cause." — John 15:25 (ASV)

But this cometh to pass (αλλ'). Ellipsis in the Greek (no verb), as in 9:3; 13:18.

In their law (εν τω νομω αυτων). Cf. 8:17; 10:34 for this standpoint. "Law" (νομος) here is for the whole of Scripture as in 12:34. The allusion is to Ps 69:4 . The hatred of the Jews toward Jesus the promised Messiah (1:11) is "part of the mysterious purpose of God" (Bernard) as shown by ινα πληρωθη (first aorist passive subjunctive of πληροω, to fulfil).

Without a cause (δωρεαν). Adverbial accusative of δωρεα from διδωμ, gratuitously, then unnecessarily or gratis (in two Koine tablets, Nageli) as here and Ga 2:21.