This short, yet powerfully uplifting text is found at the end of the Avatamsaka Sutra. Here is a very good, short commentary by Lochen Dharmashri (17th cent.) that I just discovered.
The Gate of Entry into the Limitless Activities of the Supreme Noble Ones. The commentary is only 30 pages or so; 2nd printing of 2012; tr. by Khenpo Gawang Rinpoche & Gerry Wiener
I suppose there are other English commentaries in print, but I cannot think of one.