How can I keep from singing?

I've been humming this a lot recently:

My life flows on in endless song
Above earth's lamentation.
I hear the real, though far off hymn
That hails the new creation
Above the tumult and the strife,
I hear the music ringing;
It sounds an echo in my soul
How can I keep from singing?

What though the tempest loudly roars,
I hear the truth, it liveth.
What though the darkness round me close,
Songs in the night it giveth.
No storm can shake my inmost calm
While to that rock I'm clinging.
Since love is lord of Heaven and earth
How can I keep from singing?

When tyrants tremble, sick with fear,
And hear their death-knell ringing,
When friends rejoice both far and near,
How can I keep from singing?
In prison cell and dungeon vile
Our thoughts to them are winging.
When friends by shame are undefiled,
How can I keep from singing?