"Argue as much as you like, even if the plates fly that is fine, but never end the day without making peace," the pope said in Assisi Cathedral.
"If married couples learn to say sorry, that is peace... It is a nice secret and that is life, rather than painful separations," he said.
Married couples who separate "have not managed to forgive each other in time," the pope said.
The pope also told priests not to give "endless and boring homilies that no one understands".
He told them to get to know their own parishes and said he had met clerics in Argentina "who even knew the names of the dogs in each family".