Several of my unaccompanied choral compositions begin with one voice part or one solo voice singing a principle melody.
I like this type of introduction because it allowallows the beauty of a single melody to really be absorbed. Also there it leaves much room for the piece to expand musically. Perhaps best of all, if sung well, it allows the listener to easily comprehend the text.
I generally would not want an entire concert to be built with pieces that all begin this way, but this type of opening has some musical and textual advantagesadvantages.
Here are some compositions that open in this way:
Are You Ready? – TB unison
In Heaven There are Mansions – treble solo
My Prayer – male solo
Prayer and Answer – SA unison
Set Me as a Seal – SA unison
Soon One Day – B unison