Like I said, it signifies 500 years of Christianity and also it's the birth of the Philippines as we know it today. Not sure how Magellan went about it but from what I've read he immediately became friendly with a Cebu chieftain who accepted the faith unlike Lapu-Lapu the chieftain of Mactan Island who reportedly was a muslim. Lapu-Lapu then went into battle with Magellan's heavily outnumbered men, defeating them and subsequently killing Magellan in the process. Both have shrines on Mactan Island and Lapu-Lapu has a city named after him.