The best "explanation" I've read comes directly from the preface of the Canon for Mass on Sundays from the Roman Missal. You won't see this at the Ordinary Form of the Mass in its current translation.
It is indeed fitting and right, our duty and our salvation, always and everywhere to give thanks to You, Lord, Holy Father, almighty and eternal God, who with Your only-begotten Son and the Holy Spirit are one God, one Lord: Not in the oneness of a single person, but three persons in one single essence. For what we believe from your revelation concerning Your glory, that also we believe of Your Son and of the Holy Spirit without difference or distinction; so that when we affirm the true and everlasting Godhead we worship three distinct persons in a oneness of Being and with equality of majesty. And that God the angels praise with the archangels, cherubim, and seraphs, ceaselessly singing with one voice: