Honestly? I love singing. There's just something that feels good about it. And music can definitely have a real effect on the world around you. Though the Adeptus Sororitas take it to entirely new levels with their Battle Hymns. Get a look at them in this preview of their upcoming 40k book.
From the article:
In the last Battle Sister Bulletin, we met the mighty Morvenn Vahl, and this time, we’re taking a look at the tuneful melodies of the Adepta Sororitas’ Hymns of Battle. After hearing the grating electronica of the Adeptus Mechanicus, it’s fair to say the Sisters of Battle prefer something a little more… traditional.
They’ve already got accompaniment in the form of the Exorcist, so these devout warriors can move their enemies to tears with a dirge in the minor key of suffering. Open your hymn books to page 73, and we’ll take a look.