Q: In the general presentation of the Liturgy of the Hours, No. 123, it says: “The custom of concluding the psalm with Glory be to the Father is retained. Tradition has aptly employed this to attribute to the prayer of the Old Testament a quality of praise and a christological and trinitarian meaning.” And in No. 137, we learn that “At Vespers, after the two psalms, a canticle from the Epistles or Revelation of the New Testament is inserted. There are seven such canticles, one for each day of the week.” Here is my concern: Since these canticles are not neither psalms nor from the Old Testament to apply automatically to what is said in No. 123, can we also conclude these canticles of the New Testament with Glory be to the Father as in any psalm recited or sung?
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A: You are correct that the General Instruction does not mention reciting the Glory to the Father at the conclusion of the New Testament canticles. In my experience, it is commonly done. GILH does not limit the Glory to the Father to the Old Testament—it just ensures that it will happen in those instances.
Given the widespread custom, I see no problem with adding it to the New Testament canticle, but it would be hard to say it is required.