Not only will Yahwe reign forever, but Yahwe has been reigning from the beginning:
Established is thy throne of old.
—Psalm 93:2.
Yahwe sat at the flood,
Yea Yahwe sitteth as king forever.
—Psalm 29:10.
It is perhaps important for Old Testament scholarship to bear in mind that the conception of the deity as king is so very old, and that it is present in the biblical hymns which can not be classed as eschatological. It is in Psalm 103 that one finds the words:
Yahwe in the heavens hath established his throne,
And his kingdom ruleth over all
and in Psalm 95 which can not be called eschatological, we have: