Obj. 4. Further, In the Old Law God was praised with musical instruments and human song, according to Ps. 32:2, 3: “Give praise to the Lord on the harp, sing to Him with the psaltery, the instrument of ten strings. Sing to Him a new canticle.” But the Church does not make use of musical instruments, such as harps and psalteries, in the divine praises, for fear of seeming to imitate the Jews. Therefore in like manner neither should song be used in the divine praises.
On the contrary, Blessed Ambrose established singing in the Church of Milan, as Augustine relates (Conf. ix.).
Reply Obj. 4. As the Philosopher says (Polit. viii.), Teaching should not be accompanied with a flute or any artificial instrument such as the harp or anything else of this kind: but only with such things as make good hearers. For suchlike musical instruments move the soul to pleasure rather than create a good disposition within it. In the Old Testament instruments of this description were employed, both because the people were more coarse and carnal—so that they needed to be aroused by such instruments as also by earthly promises—and because these material instruments were figures of something else.
—Thomas Aquinas (c. 1224–74), Summa Theologica, trans. Fathers of the English Dominican Province (Bellingham, WA: Logos Bible Software, 2009), 2.2.91.