VATICAN CITY, OCT. 2, 2002 ( Given the ups and downs of daily existence, trust in God is the only "eternal Rock" on which the life of every person can be based, John Paul II says.

This is the message the Holy Father gave during today's general audience in St. Peter's Square, which drew more than 15,000 pilgrims and tourists. He dedicated his address a commentary on Chapter 26 of the Book of Isaiah.

The hymn is the "joyous celebration of the city of salvation" of which "the Lord himself has laid the foundations and the walls of defense, rendering it a safe and tranquil dwelling," the Pontiff explained.

Continuing with his series of meditations on the Psalms and canticles of the Jewish people, the Holy Father explained that this image posits two opposing cities: "the rebellious city, incarnated in some historical centers of that time, and the holy city, where the faithful gather."

In the latter, God "opens wide the gates to receive the righteous people." But, the Pope added, "whoever enters the city of salvation must have an essential requisite" -- trust in God.

"It is faith in God, a solid faith based on him, who is an eternal rock," the Holy Father said.

This biblical passage chosen by the Holy Father caught the attention of the Fathers of the Church, who forged Christian thought in the early centuries: "In that promise of peace they discerned the words of Christ that would resound centuries later: 'Peace I leave with you, my peace I give to you.'"

The Pope quoted St. Cyril of Alexandria (376-444), who prayed: "Grant us peace, O Lord. Then we will admit we have everything, and it will seem to us that he who has received the fullness of Christ does not lack anything. Indeed, the fullness of every good is the fact that God dwells in us by the Spirit."

With this conviction, the Pope concluded, the Christian can face "the new day" with "his spirit reassured."