The Church Music Association of America has put the latest issue of Sacred Music (Volume 133.1) online, as this post explains. It features a piece by William Mahrt, the new editor. He explains how and why chant is the ideal form of liturgical music. He provides a close examination of a single liturgical text employed in three different uses in the Roman Rite and uses the structure of each melody to illustrate a theological point.
The article will be a revelation for anyone who thinks of the liturgy as a text-only enterprise, or anyone who believes that the Roman Rite can be fully understood apart from its official chant books. The issue also contains articles on the Ward Method, William Byrd's "Ave Verum," and other essays and documents.
Subscriptions come with membership.
Coda: I should have mentioned that the entire issue is available for free online. If you join the CMAA, you can get this issue in the mail (with a cover suitable for framing!)