He did not appear to be in pain as he gave the address standing before a lectern and frequently improvising his remarks.
The pope reflected on Sunday's Gospel reading, Mark 1:14-20, in which Jesus takes up the call to repentance first issued by St. John the Baptist. He said that Christ's message contained two fundamental themes: time and conversion.
"The time of salvation is fulfilled because Jesus has arrived. However, salvation is not automatic; salvation is a gift of love and as such offered to human freedom," he said, noting that to receive this gift we must be open to conversion.
"It means to change mentality -- this is conversion, to change mentality -- and to change life: to no longer follow the examples of the world but those of God, who is Jesus; to follow Jesus, as Jesus had done, and as Jesus taught us. It is a decisive change of view and attitude," he said.
He explained that an opposing force -- sin -- encourages us to affirm ourselves at the expense of others and God. This worldly mentality, he said, leads to deception and violence.
"This is the mentality of deceit that definitely has its origins in the father of deceit, the great pretender, the devil. He is the father of lies, as Jesus defines him," he commented.
In contrast, Jesus invites us to recognize our need for God and his grace.
The 84-year-old pope said: "For each one of us the time in which we are able to receive redemption is brief: it is the duration of our life in this world. It is brief. Perhaps it seems long..."
He recalled giving the last rites to a "very good elderly man."
"Before receiving the Eucharist and the Anointing of the Sick, he said this phrase to me: 'My life has flown by,' as if to say: I believed that it was eternal, but... 'my life has flown by.'"
"This is how we, the elderly, feel that life has passed away. It passes away. And life is a gift of God's infinite love, but is also the time to prove our love for Him. For this reason every moment, every instant of our existence, is precious time to love God and to love our neighbor, and thereby enter into eternal life."
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The pope stressed that each phase of our lives can be "a privileged moment of encounter with the Lord."
"Dear brothers and sisters, let us stay attentive and not let Jesus pass by without welcoming him. St. Augustine said, 'I am afraid of God when he passes by.' Afraid of what? Of not recognizing him, of not seeing him, of not welcoming him."
"May the Virgin Mary help us to live each day, each moment, as the time of salvation, in which the Lord passes and calls us to follow him, every second of our life. And may she help us to convert from the mentality of the world, that of worldly reveries which are fireworks, to that of love and service."
After reciting the Angelus, the pope noted that Jan. 24 is the Sunday of the Word of God. He was unable to celebrate a morning Mass marking the occasion in St. Peter's Basilica due to sciatica. The Mass was offered instead by Archbishop Rino Fisichella, president of the Pontifical Council for Promoting the New Evangelization.
But the Holy See press office said on Sunday that the pope was able to give a special edition of the Bible to people representing various states of life in the Catholic Church. The presentation took place at the pope's residence, the Casa Santa Marta, instead of at the Basilica as planned.