This seems to me a good example of the free floating choruses and exclamations that were apparently prevalent in the 19th century camp meetings and other revival activities.

The Sacred Harp has an example that uses the Trumpet sound motif as both an interjection in a basic 4 line hymn and then adds a chorus.

Pilgrim Productions has a recording of it.

The Morning Trumpet
85
Tune: B. F. White, 1844
Lyrics: John Leland, 1793
Meter: 7s,6s (7,6,7,6)

Oh when shall I see Jesus,
And reign with Him above,
And shall hear the trumpet sound in the morning?
And from the flowing fountain
Drink everlasting love,
And shall hear the trumpet sound in the morning?

Chorus:

Shout, Oh glory! for I shall mount above the skies,
When I hear the trumpet sound in the morning.

When shall I be delivered
From this vain world of sin,
And shall hear the trumpet sound in the morning?
And with my blessed Jesus,
Drink endless pleasures in,
And shall hear the trumpet sound in the morning?

(Chorus)

But now I am a soldier,
My Captain's gone before;
He's given me my orders,
And bids me ne'er give o'er;

His promises are faithful --
A righteous crown He'll give,
And all His valiant soldiers
Eternally shall live.

Through grace I feel determined
To conquer, though I die,
And then away to Jesus
On wings of love I'll fly;

Farewell to sin and sorrow,
I bid them both adieu!
And, Oh my friends, prove faithful,
And on your way pursue.

Whene'er you meet with troubles,
And trials on your way,
Then cast your care on Jesus,
And don't forget to pray.

Gird on the gospel armor
Of faith, and hope, and love,
And when the combat's ended,
He'll carry you above.

Oh do not be discouraged,
For Jesus is your Friend;
And if you lack for knowledge,
He'll not refuse to lend.

Neither will He upbraid you,
Though often you request,
He'll give you grace to conquer,
And take you home to rest.