Responsorial Psalm (Psalm 138)
R.    In the sight of the angels I will sing your praises, Lord. 
I will give thanks to you, O LORD, with all my heart,
 for you have heard the words of my mouth;
 in the presence of the angels I will sing your praise; I will worship at your holy temple
 and give thanks to your name.
 R.    In the sight of the angels I will sing your praises, Lord.

In the Divine Liturgy of Saint John Chrysostom we learn that in the celebration of the Eucharist we are like the angels in that we represent the Cherubim and we sing the song of the Seraphim, who sing Holy, Holy, Holy:

Let us, who mystically represent the Cherubim and who sing the thrice-holy hymn to the life-creating Trinity, now lay aside every worldly care. So that we may receive the King of all . . . Who is invisibly escorted by the angelic hosts. Alleluia. Alleluia. Alleluia.