38 Therefore when We praised the manifold power and the apostolic effectiveness of sacred music, We spoke of something that can be a source of great joy and solace to all who have in any way dedicated themselves to its study and practice. All who use the art they possess to compose such musical compositions, to teach them or to perform them by singing or using musical instruments, undoubtedly exercise in many ways a true and genuine apostolate. They will receive from Christ the Lord the generous rewards and honors of apostles for the work they have done so faithfully.
Source: Musicae Sacrae (Vatican.va)