Pope Francis has warned Catholics to beware people who will look to profit from their faith after police seized fake parchments worth an estimated £50,000 from a souvenir shop near the Vatican.
Rome's financial police have placed 35 officers on operation Jubilaeum, which aims to counter the influx of traders looking to make a profit out of Jubilee Year.
Speaking to his weekly general audience in St Peter's Square, Pope Francis told pilgrims: "Be careful! Beware of someone who is sly or sneaky who tells you that you need to pay. Salvation cannot be paid for, salvation cannot be bought. Jesus is the door and Jesus is free of charge."
Prior to the start of the Jubilee Year, Archbishop Rino Fisichella, president of the Pontifical Council for the Promotion of the New Evangelization, said pilgrims must be vigilant not only of terrorist threats but also of scam artists who see the Holy Year as "a source of income".
"It's not just about security for fear of Isis. There has to be security to watch out for people's dignity," he told journalists.
During his address, Pope Francis expressed his hope that the Holy Year celebrations in dioceses across the globe would serve as "a visible sign of universal communion" and of God's love and mercy to the world.
Noting that the start of the Holy Year coincides with the 50th anniversary of the conclusion of the Second Vatican Council, the pope said that the council highlighted this "mystery of communion" among the churches worldwide.
"Although spread throughout the world and divided into many particular churches, it has always been the one and only church that Jesus Christ wanted and for whom he offered himself," he said.
The Holy Door is a symbol of Jesus Christ, he said, and pilgrims who pass through it in Rome and in churches around the world make a visible sign of trust in him "who did not come to judge but to save".
"It is a sign of a true conversion of the heart," the pope said. "When we pass through that door, it is good to remember that we should also open wide the doors of our heart."
Confession, he continued, is another important aspect of the Holy Year that gives the faithful the opportunity to have "a direct experience" of mercy. However, one must first recognise their sins and also forgive others in order to fully experience God's love and forgiveness.
"When we recognise our sins and ask forgiveness, there is a celebration in heaven; Jesus celebrates," Pope Francis said. "This is his mercy; do not be discouraged, go forward."
Before the start of the audience, pilgrims sang "Happy Birthday" to the pope who will celebrate his 79th birthday on Thursday.
As he made his way to the stage, veteran Mexican journalist, Valentina Alazraki, presented Pope Francis with a sombrero-shaped birthday cake on behalf of the Mexican people.