The source tune is 'Deo Gracias' - 15th c. - English.
I had in mind this (fairly) well known Epiphany Text (also originally 15th c. [Latin]):
O wondrous type! O vision fair
of glory that the Church may share,
which Christ upon the mountain shows,
where brighter than the sun he glows!
The law and prophets there have place,
the chosen witnesses of grace;
the Father's voice from our the cloud
proclaims his only Son aloud.
With shining face and bright array,
Christ deigns to manifest today
what glory shall be theirs above
who joy in God with perfect love.
And faithful hearts are raised on high
by this great vision's mystery;
for which in joyful strains we raise
the voice of prayer, the hymns of praise.
O Father, with the eternal Son,
and Holy Spirit, ever One,
vouchsafe to bring us by thy grace
to see thy glory face to face.
I am looking to portray the wonder, and - humanly speaking - uncertainty of Theophany: What were Peter, James, and John thinking on the Mount of Transfiguration? Besides just 'shock and awe'… What of Moses and the Burning Bush? And of course (I beg) the question: Do we experience our own moments of Theophany and if so what is our reaction to them.*
* The above 'religious' chit chat is an attempt to share my compositional thought process. No offense is intended to those of differing perspectives. Thanks in advance for your indulgence!