Pope Benedict said his heart was filled with gratitude "for the 90 years the good Lord has given me. There have been trying and difficult times, but he always guided me and pulled me through."
The 460-page commemorative volume gathers just a slice of the kind of rigorous research still being done today "in the light of faith," and in the footsteps of a 90-year-old pope.
The invitation came amid increasingly closer relations between the Vatican and al-Azhar University, which is considered the most authoritative theological-academic institution of Sunni Islam.
The answer to the refugee crisis is continued assistance "not to close the gates of the countries where people are knocking for survival," Archbishop Silvano M. Tomasi said.