The answer is: Thousands upon thousands of angels

Rev 5 vs 11-12

In Revelation 5, we witness an awe-inspiring scene in the heavenly throne room where the angels extend their praises to the Lamb. This whole chapter serves as a sort of celestial courtroom drama where a scroll, holding the destiny of humankind, can only be opened by the worthy one—the Lamb who was slain. The chorus from the thousands upon thousands of angels declaring, “Worthy is the Lamb who was slain,” not only exemplifies their exaltation of Jesus but also highlights a key theme of immense sacrifice and redemption throughout the Scriptures.

It's fascinating to note that this declaration echoes a deep-rooted biblical tradition using the image of a lamb, stretching back to the Passover in Exodus where lambs were sacrificed, symbolizing rescue and redemption. Just as the blood of the lamb saved the Israelites, here we find the Lamb on a cosmic scale, signifying a broader release from the shackles of sin and death.

And let’s not forget some interesting trivia: the numerical phrase "thousands upon thousands" suggests an overwhelming multitude, providing a visual image of unity and harmony. The number also reflects back to God's infinite glory and should remind us of the multitude of divine and angelic believers reported in other key parts of the Bible. Essentially, whenever angels speak, and songs of praise ring, it echoes the ultimate truth in many other scripture passages — significant salvation comes through its radical examples of humility, sacrifice, and transformation. Your viewing of biblical texts can cultivate a deeper appreciation for these universals that resonate through centuries!