There's speculation that the attacks were targeting the head of Egypt's Coptic Church, Pope Tawadros II,
because he was leading the service. He ended up not being injured, though.
Also, in their claim of responsibility, ISIS warned of more attacks with this message:
The Crusaders and their tails from the apostates must be aware that the bill between us and them is very large and they will be paying it like a river of blood from their sons, if God willing.
Lol, if the "Crusaders" they're referring to are the Coptic Christians, then that's hilariously inaccurate. Evidence suggests that Copts are actually the descendants of the original Egyptians (unlike most Muslim Egyptians, who are descended from
the Arabs who invaded Egypt in the mid-600s). The Egyptian Church, which is more than 1,900 years old, is most likely the oldest Christian church in the world; it's traditionally believed that it was founded by St. Mark at around 42 AD. For centuries,
Egypt was one of the Christian world's biggest and most important strongholds. However, the
Arab invasion of Egypt set off a chain of Islamization and Arabization that led to most of Egypt becoming Muslim by the 12th century. The Copts of today are the ones whose ancestors refused to convert.
What I'm getting at are that Egyptian ISIS members are retards who don't even realize that
they're the foreign invaders; they follow Wahhabism/Salafism, a cancerous ideology that was invented a couple hundred years ago in Saudi Arabia. Meanwhile, the Copts have had their roots in Egypt for nearly 2,000 years, long before Islam was even born.