Motet "Veni sancte Spiritus" by the great medieval English composer, John Dunstable (or Dunstaple), (c. 1390 – 24 December 1453). He followed his patron, the Duke of Bedford, to France with the English army, and arguably kick-started the entire Burgundian School of composition. We know he was popular because copies of his work show up in monasteries and libraries all over Europe.
Are these the lyrics?
Come Holy Spirit, Creator Blest (Veni, Creator Spiritus)
Come, Holy Spirit, Creator blest,
and in our souls take up Thy rest;
come with Thy grace and heavenly aid
to fill the hearts which Thou hast made.
O comforter, to Thee we cry,
O heavenly gift of God Most High,
O fount of life and fire of love,
and sweet anointing from above.
Thou in Thy sevenfold gifts are known;
Thou, finger of God’s hand we own;
Thou, promise of the Father, Thou
Who dost the tongue with power imbue.
Kindle our sense from above,
and make our hearts o’erflow with love;
with patience firm and virtue high
the weakness of our flesh supply.
Far from us drive the foe we dread,
and grant us Thy peace instead;
so shall we not, with Thee for guide,
turn from the path of life aside.
Oh, may Thy grace on us bestow
the Father and the Son to know;
and Thee, through endless times confessed,
of both the eternal Spirit blest.
Now to the Father and the Son,
Who rose from death, be glory given,
with Thou, O Holy Comforter,
henceforth by all in earth and heaven. Amen.