The devotion is featured in numerous books for tourists planning a visit to the Philippines. It is probably the best known folk Catholic devotion in the Philippines. Of course it isn't the only one. Each and every town in the country has probably a folk Catholic devotion.
The Nazarene devotion is what may be said as a functional one. Many folk Catholic devotions dating back to the Spanish colonial period have died out with political and social changes. The public devotions in Intramuros churches are now extinct, having gone with the destruction of the churches in WWII. Some have been revived, like the Marian processions on Dec 8. The Nazarene devotion is notable that it survived wars and revolutions. It dates back to the 1600s for the Nazarene icon itself came from Mexico brought by Recollect fathers. Tradition says that the statue is black since the ship carrying it burned down.
The networks have interviewed devotees asking their reasons why they believe. Many have expressed thanks to the Nazarene for recovery from serious illness, reforming errant children, recovering errant lovers!, blessings and prosperity, employment and even fecundity. One even gave thanks for recovering lost data from a computer!
Since the Nazarene seems to answer all prayer requests of whatever nature, it is no wonder that the devotion has retained its functionality thorough the centuries.
Some people say that people who have the devotion are "desperate". To which I say, all people on this planet are desperate. We are desperate for 1) God's presence, 2) God's peace and 3) God's healing. The devotion is a way for people to express their solidarity with the atonement of the suffering Christ.
Thus if we view it in this way, the devotion shows its real worth. It may be simplistic and crude to the theologically sophisticated but as we read in the Gospels in the tale of the woman with a flow of blood. The despised woman said
"If I only touch his cloak, I will be healed." Matthew 9:21
That probably summarizes in its entirety the Gospel foundations of the Black Nazarene devotion. No wordy theological discourse there.