It is a truism in musical theatre, (apart from opera, which is through composed,) when our emotions are too “big” to be spoken, we must sing them.
St Ambrose knew that:
Moses, when he related the deeds of the patriarchs, did so in a plain and unadorned style. But when he had miraculously led the people of Israel across the Red Sea… he transcended his own skills (just as the miracle had transcended his own powers) and he sang a triumphal song to the Lord. Miriam the prophetess herself took up a timbrel and led the others in the refrain: Sing to the Lord: he has covered himself in glory, horse and rider he has thrown into the sea.
History instructs us, the law teaches us, prophecy foretells, correction punishes, morality persuades; but the book of psalms goes further than all these. It is medicine for our spiritual health. Whoever reads it will find in it a medicine to cure the wounds caused by his own particular passions ..And as for the power of prophecy – what can I say? Other prophets spoke in riddles. To the psalmist alone, it seems, God promised openly and clearly that the Lord Jesus would be born of his seed: I promise that your own son will succeed you on the throne.Thus in the book of psalms Jesus is not only born for us: he also accepts his saving passion, he dies, he rises from the dead, he ascends into heaven, he sits at the Father’s right hand. The Psalmist announced what no other prophet had dared to say, that which was later preached by the Lord himself in the Gospel.
As true of opera, I'd say. Figaro puts it a little differently: https://en.wikiquote.org/wiki/Voltaire#Misattribu…
Touche!
It is true that "Nowadays what isn't worth saying is sung" (Figaro), as has been demonstrated in song as well as opera. But the obverse is also true: what is worth saying can be said better by singing. This is particularly true of the liturgy.