Leaf of manuscript at First Free Methodist Church, Seattle

benedicimus ti
bi gloria in secu
la.  ps. Magnt.
Et fit co
memor
Domini
nice prie
Antiph.
Nolite iudi
care ut non iudi

     Leaf of a 16th- or 17th-century Roman Breviary (more strictly an Antiphonal or Antiphonary) opened to Second Vespers, Trinity Sunday.  Fine Center, First Free Methodist Church, Seattle, WA.  (Neither the "text" nor the "author" of this manuscript can therefore be said to be any longer "unknown".)

• . . . benedicimus tibi gloria in s(a)ecula.  Concluding fragment (or explicit) of the Te deum patrem ingenitum, of which there are examples in CANTUS from c. 980 (Sankt Gallen, Stiftsbibliothek, 390 (CH-SGs 390)), all of them either Antiphons or Responsories, and the vast bulk of them associated with either First or Second Vespers on Trinity Sunday: "Te deum patrem ingenitum te filium unigenitum te spiritum sanctum paraclitum sanctam et individuam trinitatem toto corde et ore confitemur laudamus atque benedicimus tibi gloria in saecula," "Thee God the Father unbegotten, thee the only begotten Son, thee the Holy Ghost the Comforter, holy and undivided Trinity, with all our heart and mouth we confess, praise and bless; to thee be glory for ever" (trans. Margaret Winkworth).
• ps[almus (a rubric)].  Magn[ifica]t.

• Et fit com(m)emor[atio] Domininic[a]e pri[ma]e Antiph[ona (a rubric)].  "Then is made a commemoration of the First Sunday [after Pentecost]".  See, for example, First Vespers, Trinity Sunday, in the 1893 Breviary below ("Et fit Commemoratio Dominicæ primæ post Pentecosten, Aña", "Then is made a commemoration of the First Sunday after Pentecost, [with the] Antiphon" Loquere Domine, quia audit servus tuus), though the Antiphon in the case of Second Vespers is Nolite judicare, below.  "the feast [of Pentecost] was kept with an octave from early times" (ODCC, 3rd rev. ed., s.v. "Whitsunday"), and is therefore much older than the feast of the Trinity, which didn't become a feast of the universal Church until 1334, but was at that point (?) assigned to the First Sunday after Pentecost (though the Sundays following continued to be reckoned as "after Pentecost" ("Second Sunday after Pentecost" and so forth) rather than "after Trinity" ("First Sunday after Trinity" and so forth) in the Roman rite (the Carmelite, Dominican, and Carthusian orders excepted) until 1969) (ODCC, 3rd rev. ed., s.v. "Trinity Sunday").
• Nolite iudicare ut non iudi[cemini]:  Mt 7:1, Vulgate, also used frequently as an antiphon (Cantus from c. 980, according to which the Nolite iudicare gets associated with Trinity Sunday (rather than, say, the Fourth or Fifth Sunday after Pentecost) several centuries later than the Te deum patrem ingenitum (1400 and 1501)):  "Judge not, that you be not jud[ged]."

     If this leaf-of-a-manuscript is really from the 16th or 17th century, then the relevant major revisions to the Breviarium Romanum were made in 1568 and 1911, and this 1893 printing of the Breviary (opened to Second Vespers, Trinity Sunday) ought to be roughly what we're looking for.  Note that it makes the Te deum patrem ingenitum the Antiphon to the Magnificat ("Ad Magnif. Aña."), and the Nolite judicare, the Antiphon for the commemoration of the Pentecostal background to Trinity Sunday ("Pro Commem. Dominicæ, Aña.", "For the Commemoration of the [First] Sunday [after Pentecost], [use the] Antiphon" Nolite judicare).  Cf. this 1879 printing of a translation of the pre-1911 Roman Breviary into English, at Second Vespers, Trinity Sunday:  "Antiphon at the Song of the Blessed Virgin.  With all our heart and with all our voice do we acknowledge Thee, praise Thee, and bless Thee, O God the Father the Unbegotten. . . . The following is the Commemoration of the First Sunday after Pentecost.  Antiphon.  Judge not, that ye be not judged. . . . Verse. . . . Answer. . . . Prayer. . . ."

     On pp. 1445-1446 of vol. 2 of The hours of the Divine Office in English and Latin (Collegeville, MN:  The Liturgical Press, 1964), the Te Deum Patrem ingenitum is still the Antiphon to the Magnificat for Second Vespers, but "There is no commemoration of the Sunday."  And in the post-Vatican II Liturgia horarum, there isn't even that, let alone the Nolite judicare, but only the Te Deum Patrem ingenitum in that same position:

Ad Magnificat, ant. Te Deum Patrem ingenitum, te Filium unigenitum, te Spiritum Sanctum Paraclitum, sanctam et individuam Trinitatem, toto corde et ore confitemur, laudamus atque benedicimus: Tibi gloria in sæcula.

Canticle of Mary 

Ant.  With our whole heart and voice we acclaim you, O God; we offer you our praise and worship, unbegotten Father, only-begotten Son, Holy Spirit, constant friend and guide; most holy and undivided Trinity, to you be glory for ever. 

     In conclusion, what First Free Methodist has appears to be the leaf of a Roman Breviary (but given the presence of musical notation, more strictly an Antiphonal or Antiphonary) opened to the middle of Second Vespers, Trinity Sunday.

     I make at present no claims as to authenticity of the artifact itself.  Note, for example, that "Dominic[a]e" is mispelled ("Domini|nic[a]e" being an example of dittography).

     With thanks to Dr. Owen Ewald for his input.