Expressing passion can be a good thing or it can also be bad. It's sort of like money, which is not the root of all evil--its the LOVE of money that is--so money is used good or bad based on the character in whose hands its managed. We have passions. Passion of our flesh equals a desire to express a strong feeling or emotion, express our opinion with great force, or see a need or injustice and are so moved we blindly go forward to do what we feel is the right thing to do.
Orpah clearly had enough sense of duty to her mother-in-law to come along with Ruth when they helped pack up and leave Moab. But Naomi kept giving them the option to go back...the reason being was that to go on to Bethlehem Judah would be a true test of endurance with no obvious guarantees--and would require a much higher level of discipline to remain in the camp of the people of God. Orpah took the road back to her people, her gods, and to the place where she didn't have to live up to the standard of pursuit that would be required of Naomi. Ruth however chose to humble herself and pursue. Did she have weaknesses? I imagine such a person to passionately express her feelings to Naomi probably had passionately expressed her opinion before! But a definite change must have occurred in her own character at the death of her husband as much as it did for Naomi to lose both husband and sons. And now they leave all they know--Ruth moreso as it was her home country--to pursue redemption.
We must daily pursue our Savior Jesus if we ever expect Him to become our Lord and Master. Sometimes it means we must, like Ruth, choose to depart from everything that has been like Moab in our life...or as Jesus said in Matthew 10:39, " Whoever finds his life will lose it, and whoever loses his life for my sake will find it"