Charles H. Spurgeon on Psalms 50:6

And the heavens shall declare his righteousness. Celestial intelligences and the spirits of just men made perfect, shall magnify the infallible judgment of the divine tribunal. Now they doubtless wonder at the hypocrisy of men; then they shall equally marvel at the exactness of the severance between the true and the false. For God is judge himself. This is the reason for the correctness of the judgment. Priests of old, and churches of later times, were readily deceived, but not so the all discerning Lord. No deputy judge sits on the great white throne; the injured Lord of all himself weighs the evidence and allots the vengeance or reward. The scene in the Psalm is a grand poetical conception, but it is also an inspired prophecy of that day which shall burn as an oven, when the Lord shall discern between him that feareth and him that feareth him not. Selah. Here we may well pause in reverent prostration, in deep searching of heart, in humble prayer, and in awe struck expectation.

Verses 7-15. The address which follows is directed to the professed people of God. It is clearly, in the first place, meant for Israel; but is equally applicable to the visible church of God in every age. It declares the futility of external worship when spiritual faith is absent, and the mere outward ceremonial is rested in.