Tradition
St. Augustine
The Enarrations, or Expositions, on the Psalms
Psalm 100 › Section 1
1. You heard the Psalm, brethren, while it was being chanted: it is short, and not obscure: as if I had given you an assurance, that you should not fear fatigue....
Source: The Enarrations, or Expositions, on the Psalms (New Advent)