The true office of the soft palate is to modify the opening into the nose and thus attune the resonant cavities to the pitch and timbre of the note given by the vocal cords and pharynx.

To develop the vowel sounds, the soft palate should be drawn forward, allowing a free passage into the nose; it should be closed only to form the consonants which require a forcible expulsion of breath from the mouth.
The uvula, the pendulous tip of the soft palate, serves as a valve to more accurately adjust the opening behind the soft palate to the pitch of the voice.

In producing a low tone the soft palate is relaxed and hangs low down and far forward.

As the voice ascends the scale the tension of the soft palate is increased and it is elevated and the uvula shortened, thus decreasing the opening behind the palate, but never closing it.

In fact the larger the opening that can be maintained, the broader and better the tone.