So, we'll go no more a-roving
So late into the night,
Though the heart be still as loving,
And the moon be still as bright.
For the sword outwears its sheath,
And the soul wears out the breast,
And the heart must pause to breathe,
And Love itself have rest.
Though the night was made for loving,
This echoes the previous line, implying that the spiritual man, the speaker, is still prepared for the challenge of life, but the ‘breast’, or the physical being, is exhausted, or worn out. 
 Note the two lines are  syntactic parallels , the second time Byron has used this device. It sustains the rhythm and the sense that, beneath the weariness, there is still vitality.
So well go no more a-roving