"We must respond worthily to so great a gift, that is to say, with the gift of ourselves, our time, our prayer, our entering into a profound communion of love with Christ who suffered, died and rose for us," Pope Benedict said.

Tens of thousands of people gathered for the Mass under overcast skies. Pope Benedict arrived in an open popemobile behind a procession of young people carrying whole palm fronds, priests carrying olive branches -- the traditional Palm Sunday symbol in Italy -- and bishops and cardinals carrying tall, braided palms.

In his homily, Pope Benedict said the disciples and crowds who followed Jesus to Jerusalem had their own idea of who Jesus was and what difference he would make in their lives and the life of Israel.

In fact, he said, the vast majority of them were disappointed he did not live up to their expectations and they went -- in a space of a few days -- from acclaiming him as Messiah as he entered Jerusalem to calling for his crucifixion or running away frightened.

In the same way, Christians today must ask themselves, "Who is Jesus of Nazareth for us? What idea do we have of the Messiah, what idea do we have of God?" the Pope said.

The question is key at the beginning of Holy Week, when "we are called to follow our king who chooses the cross as this throne," he said.

"We are called to follow a messiah who promises us, not a facile earthly happiness, but the happiness of heaven," the Pope said.

Directing his remarks particularly to young people marking the diocesan-level celebration of World Youth Day, Pope Benedict said Palm Sunday should be a day for making a clear decision, "the decision to say 'yes' to the Lord and to follow him all the way, the decision to make his Passover, death and resurrection the very focus of your Christian lives."