Charles H. Spurgeon on Psalms 89:5

And the heavens shall praise thy wonders, O Lord. Looking down upon what God had done, and was about to do, in connection with his covenant of grace, all heaven would be filled with adoring wonder. The sun and moon, which had been made tokens of the covenant, would praise God for such an extraordinary display of mercy, and the angels and redeemed spirits would sing, "as it were, a new song." Thy faithfulness also in the congregation of the saints. By which is probably intended the holy ones on earth. So that the "whole family in heaven and earth" would join in the praise. Earth and heaven are one in admiring and adoring the covenant God. Saints above see most clearly into the heights and depths of divine love, therefore they praise its wonders; and saints below, being conscious of their many sins and multiplied provocations of the Lord, admire his faithfulness. The heavens broke forth with music at the wonders of mercy contained in the glad tidings concerning Bethlehem, and the saints who came together in the temple magnified the faithfulness of God at the birth of the Son of David. Since that auspicious day, the general assembly on high and the sacred congregation below have not ceased to sing unto Jehovah, the Lord that keepeth covenant with his elect.