Sacred or Secular?

I am in the process of preparing for some solo recitals and possibly getting back into the seasonal soiree's so encompassing for performing artists. What a relentless conundrum of exhaustive practicing and meticulous technical work!
In the course of this re-development of the musical arts, I am in a quandry as to what actually denotes sacred and secular music/performances and actions. Posting to the internet I have asked for input on these concepts and a bit of the discussion (with annotations in the proper places) seems appropriate at this time.
Let's take the Mozart Clarinet Concerto, K. 622 for Clarinet in A. The second movement is considered a movement full of melancholy and very intense emotions when performed a certain way. Is that what Mozart intended for this movement? Perhaps, looking at it from a different aspect, it can be interpreted as a movement showing love and adoration of a spiritual nature for expression on the concert stage around the world, or in a church service for meditation, prayer and thought about the Love of God and how it is shared.
Of course, there is the cadenza in the middle of the piece, where it is left up to the performer to give their own interpretation, unaccompanied, of the thematic materials of the piece or the freedom to interject various aspects of the spirit of the day in which it is performed.
I am considering, for a sharing experience in the sacred service of life at church the following, for the cadenza, a Pete Fountain, jazzy rendition of "Just A Closer Walk With Thee" or some some other soulful and fulfilling interjection of spirtual faith and love.
A bit out of character with the Concerto itself? Perhaps not, who's to know, so I ask the question of anyone out there, "What Would Mozart Do?"