By James Mackenzie
ROME (Reuters) - Pope Benedict preached a message of unity as he opened Holy Week celebrations on Palm Sunday before tens of thousands of faithful packed into St Peter's Square.
Just back from a six-day visit to Mexico and Cuba, the 84-year-old pontiff on Saturday learnt that communist Cuba had agreed to his request of declaring Good Friday a holiday this year.
In a homily built on the story of Jesus' entry into Jerusalem the week before he was crucified, Benedict said the underlying resonance of the Easter celebration was the shared destiny of humanity.
"Here we find the first great message that today's feast brings us: the invitation to adopt a proper outlook upon all humanity, on the peoples who make up the world, on its different cultures and civilizations," he said.
Clad in a red and gold robe, the pope led the service before dozens of bishops and cardinals as well as pilgrims holding palm and olive leaves to commemorate the branches said to have been laid down before Jesus as he rode into Jerusalem on a donkey.
The German pontiff, who celebrates his 85th birthday on April 16 and who has appeared frail, now faces an intense week of church celebrations.
The celebrations on Palm Sunday, a moveable feast held on the first Sunday before Easter, mark the start of Holy Week, leading up to Easter Sunday, the most important date in the church calendar.
On Holy Thursday, he will celebrate two masses in the Vatican, during one of which he will kiss and wash the feet of 12 men, in a gesture celebrating Jesus' humility towards his apostles on the night before he died.
On Good Friday, the day which marks the crucifixion of Jesus, the pope will lead services in the Vatican before heading the traditional "Via Crucis", the torch-lit "Way of the Cross" around the ancient Colosseum in Rome.
Holy Week culminates on Easter Sunday, when Christians celebrate the resurrection of Jesus and when the pope gives his twice yearly "Urbi et Orbi" (the city and the world) blessing and message.
(Reporting By James Mackenzie; Editing by Andrew Osborn)