The singers and musicians.
David put those in order who were appointed to be singers and musicians in the temple. To prophesy, in this place, means praising God with great earnestness and devout affections, under the influences of the Holy Spirit. In raising these affections, poetry and music were employed. If the Spirit of God do not put life and fervour into our devotions, they will, however ordered, be a lifeless, worthless form.