Anglorum iam Apostolus
Feast of St. Gregory the Great
St. Peter Damian

To English Isles sent formerly,
Now in angelic company,
Make haste, St. Gregory, relieve
And help the people who believe.

From riches and from wealth you turned.
The glory of the world you spurned,
That you might follow, being poor,
Prince Jesus, who was poor before.

This Christ, High Pontifex, decreed
That you would take His Church’s lead,
And learn St. Peter’s steps to tread:
The rule of all called in his stead.

You wondrously solved riddles deep:
The mystic secrets Scriptures keep,
For Truth Himself has taught you these:
The lofty sacred mysteries.

O Pontifex, our leader bright,
The Church’s honor and its light,
Through dangers let them all be brought,
The ones you carefully have taught.

The unborn Father let us praise,
And to His Son like glory raise,
And to their Equal, majesty.
All glory to the Trinity. Amen

Christe pastorum
Common of Pastors, for a Pope (translation)

Christ, great high prince and leader of the shepherds,
Wishing to laud this holy pastor’s feast day
With sacred music, we acclaim his honor
singing due praises.

As once you gave the care of sheep to Peter,
So that the world might be a holy sheepfold,
So this good shepherd, raised to highest honor,
Pastures your people.

He was a guide and pattern for the sheepfold,
Light for the blind, and solace for the weary,
Good to each person, providential father--
All things to all men

Christ, who in heaven render to the holy
Crowns for their merits, help us then to follow,
That with this teacher, we may be obedient
And rise to heaven.

May equal honor celebrate the Father,
And You, O Savior, loving King forever,
And may the glory of the Holy Spirit,
Sound the world over.

Re: "To English Isles sent formerly,"

Pope St. Gregory the Great is "Apostle to the Angles" only because he sent other people than himself to the Angles -- ie, St. Augustine of Canterbury and his guys. So I'm not sure that your first line is the best way to put it.

Th'apostle to the English lands
Who now among the angels stands,
(etc)

I certainly hope the Hovhaness has been approved by the bishop in whose diocese it was published...

Lord, Receive our thankful homage (Westminster no. 204, p. 284, by Dom Bede Camm OSB)

Lord, receive our thankful homage,
Who, from toils of error freed,
Bless Thee for the hand that saved us,
And the heart that felt our need--
For Saint Gregory our father,
Vigilant in name and deed.

For our own, our dear apostle,
Gregory the Great, the Blest,
Who, while England lay in darkness,
Spared no labour, knew no rest;
For the gracious love he bore us,
Be Thy Holy Name confessed!

Love that grew, since first those children,
Fettered in a Roman mart,
With their bright young beauty won him
Help and comfort to imprat--
From that day he bore our England
Graven ever in his heart.

Lovingly he looks upon them,
Sighing, as he sets them free:
"If these little ones are Angles,
Surely angels shall they be,
Singing joyous Alleluias,
Saved from wrath, dear Lord, to Thee!"

When on Peter's throne uplifted,
All the churches claim his care,
Yet his heart is most in England
With his sons who battle there,
And he aids them in the conflict
By the arm of ceaseless prayer.

Thus our own we joy to name him,
Though our shores he never trod:
Though our sins have marred his life-work,
And we bow beneath Thy rod,
Jesu, may our father's pleading
Gain the land once more for God.

I certainly hope the Hovhaness has been approved by the bishop in whose diocese it was published...

It originally comes from an opera (I don't know the name of it, though), and Hovhaness was from the Armenian Apostolic Church (which is Orthodox), so probably not.

I searched for, but could not find the GABC for Anglorum Iam Apostolus. So, I decided to transcribe the hymn from the Liber Hymnarius (p. 427). Here it is in case it would be helpful to others:
name:Anglorum iam apostolus;
office-part:Hymnus;
mode:4;
%%
(c4) AN(f)gló(ffe)rum(d) iam(e) a(g)pós(gh)to(f)lus,(e.) (,) nunc(g) an(h)ge(g)ló(h!iwji)rum(g) so(g)ci(f)us,(h.) (;) ut(h) tunc,(h) Gre(g)gó(h!iwji)ri,(gf) gén(h)ti(h)bus,(d!ewfe.) (,) suc(e)cúr(c)re(e) iam(gfh) cre(gf)dén(g)ti(fe)bus.(e.) 2.(::) Tu(f) lar(ffe)gas(d) o(e) pum(g) có(gh)pi(f)as(e.) (,) om(g)ném(h)que(g) mun(h!iwji)di(g) gló(g)ri(f)am(h.) (;) sper(h)nis,(h) ut(g) in(h!iwji)ops(gf) ín(h)o(h)pem(d!ewfe.) (,) Ie(e)sum(c) sé(e)quá(gfh)ris(gf) prín(g)ci(fe)pem.(e.) 3.(::) Te(f) cel(ffe)sus(d) Chris(e)tus(g) pón(gh)ti(f)fex(e.) (,) su(g)æ(h) præ(g)fert(h!iwji) Ec(g)clé(g)si(f)æ;(h.) (;) sic(h) Pet(h)ri(g) gra(h!iwji)dum(gf) pér(h)ci(h)pis,(d!ewfe.) (,) cu(e)ius(c) et(e) nor(gfh)mam(gf) sé(g)que(fe)ris.(e.) 4.(::) Scrip(f)tú(ffe)rae(d) sa(e)cræ(g) my(gh)sti(f)ca(e.) (,) mi(g)re(h) sol(g)vis(h!iwji) æ(g)níg(g)ma(f)ta,(h.) (;) ex(h)cél(h)sa(g)que(h!iwji) my(gf)sté(h)ri(h)a(d!ewfe.) (,) te(e) do(c)cet(e) ip(gfh)sa(gf) Vé(g)ri(fe)tas.(e.) 5.(::) O(f) pon(ffe)ti(d)fex(e) eg(g)ré(gh)gi(f)e,(e.) (,) lux(g) et(h) de(g)cus(h!iwji) Ec(g)clé(g)si(f)æ;(h.) (;) non(h) si(h)nas(g) in(h!iwji) pe(gf) rí(h)cu(h)lis(d!ewfe.) (,) quos(e) tot(c) man(e)dá(gfh)tis(gf) ín(g)tru(fe)is.(e.) 6.(::) Sit(f) Pa(ffe)tri(d) laus(e) in(g)gé(gh)ni(f)to,(e.) (,) sit(g) de(h)cus(g) U(h!iwji)ni(g)gé(g)ni(f)to,(h.) (;) sit(h) ut(h)ri(g)ús(h!iwji)que(gf) pá(h)ri(h)li(d!ewfe.) (,) ma(e)ié(c)stas(e) sum(gfh)ma(gf) Flá(g)mi(fe)ni.(e.) (::) A(efe)men.(de..) (::)