No information is available about Villarreal, but he may have been known to Delbert A. Asay (20th c.), who served the United Methodist Church for many years as a music missionary in Uruguay and Mexico. Asay's songs and arrangements have appeared in several Hispanic songbooks, including Nuevas Canciones Cristianas, published in Uruguay (1975).
The name PASTOR (which means "shepherd") was assigned to this tune in the Psalter Hymnal. The tune consists of an antiphon (refrain) and stanzas of two identical lines that in themselves contain a phrase repeated at a lower pitch. The form of the tune exhibits similarities to the Bolivian mestizo huayno dance. Try singing the music antiphonally by dividing each stanza into either two or four segments and having everyone join in on the refrain.