Philadelphia Archbishop Charles Joseph Chaput said that the mass was the main reason for the pontiff`s trip to the United States, which will take place some five weeks before the Church`s hotly-awaited global meeting on family life.
The pope will travel to Cuba, Washington and New York before presiding over the end of the World Meeting on September 26 and 27 in Philadelphia, in what organisers are dubbing one of the biggest religious events ever held in the US.
The head of the Vatican`s Pontifical Council for the Family, Vincenzo Paglia, told journalists there was "an intimate connection" between Philadelphia and the synod, a gathering of bishops from around the world to debate family matters.
Francis hopes the synod will help reconcile Catholic thinking with the realities of believers` lives in the early 21st century, and organisers said there would be an address on the topic of homosexuality at the World Meeting of Families.
However, a first synod on the family last year saw riled conservative bishops mobilise to block the approval of language heralding an unprecedented opening to the gay community and greater flexibility on the treatment of divorced Catholics.
The Philadelphia meet will begin with a four-day congress attended by some 15,000 participants from over 100 countries, and is expected to have a $45 million dollar (40.15 million euro) price tag, largely due to security costs.
Around $30 million has already been raised for the event, Chaput said.
To mark the occasion, Francis will give away one million copies of the Gospel According to Luke, an ancient text which describes Jesus`s family.
They will be handed to the poorest families in one chosen city per continent: Marseilles in France, Kinshasa in the Democratic Republic of Congo, Havana in Cuba, Hanoi in Vietnam and Sydney in Australia.
Philadelphia will be the eighth World Meeting of Families since Jean Paul II established the tradition in 1994. Previous meetings have been held in Manila, Mexico, Milan, Rio, Valencia, and twice in the Italian capital Rome.