Psalm 50:6

And the heavens shall declare his righteousness
That is, either the heavens shall bear witness to his justice and equity in judging his people; or the angels, the ministers of the Gospel, shall declare his justifying righteousness, which is revealed in it, to the saints and covenant ones they shall be a means of gathering in: or rather the justice of Christ in the destruction of the Jews shall be attested and applauded by angels and men, just as the righteousness of God in the destruction of the antichristian powers is celebrated by the angel of the waters, ( Revelation 16:5 Revelation 16:6 ) ;

for God [is] Judge himself.
And not another, or by another; and therefore his judgments must be just and righteous, seeing he is just and true, loves righteousness, and is righteous in all his ways and works.

Selah; on this word, (See Gill on Psalms 3:2).