The concluding words of John’s
version of the song of Moses allude to Psa 98:2, of which the context is:
O sing to the LORD (שׁירו
ליהוה) a new song,
for he has done wondrous things (ופלאות עשׂה).
His right hand and his holy arm
have gotten him victory.
The LORD has made known his victory;
he has revealed his righteous acts (צדקתו) in the sight of the nations (Ps
98:1-2)
The Masoretic pointing (צִדְקָתוֹ)
gives צדקתו the meaning of ‘his righteousness’ (or ‘his vindication’) but John
has read it as צִדְקֹתָוֹ (‘his righteous acts’) and translated: τα δικαιωματα σου (15:4). (Richard Bauckham, “The Conversion of the Nations,” in
The Climax of Prophecy: Studies in the Book of Revelation [London: T&T
Clark, 1993], 304)