the Catholic Confessional Seal essentially says that Catholic priests are not allowed to disclose any information given to them during confession by the confessor. This includes whether he did or did not commit a crime, like murder. As you can imagine, this is to encourage people who have commited "Mortal Sins"- Horrible sins that can send you to hell unless you repent in confession - to come to confession and repent.
Depending on how the Church reacts, breaking said seal can lead to either losing your priestly duties or being excommunicated from the Church. Considering how devout Catholic priests have to be (They have to go through Seminary AND College to get a degree in Theology AND never get married AND become celibate), it's unlikely that many of the priests will ever agree to breaking their confessional seal.
Historically, the US government and most world governments respected the Confessional Seal, lest they incure the wrath of the Church and their faithful. There have been cases involving it, but they almost always come out in favor of the Church. That's why it's so major that this Louisiana Court continues to attempt to force the priest to break the seal despite the controversy. Now the case is being taken to the Supreme Court, which increases the stakes considerably.
I'm Catholic myself, so my own bias likely comes into play here, but here's how I see the consequences of the two possible decisions:
Yes, Courts can force priests break the Confessional Seal:
Many Catholic Priests & Some Bishops will start going to jail for refusing to break their seal. The remainder that do break the seal are stripped of their title by the Church. The Vatican will react very harshly this decision, and I wouldn't be surprised to see mass protests by the 25% of the US population that's Catholic. Criminals will stop confessing to Catholic priests for fear of being prosecuted.
No, Courts can't force priests to break the Confessional Seal:
Some Murderers, Child Molestors, Rapists, etc will continue to go free, possibly commiting more crimes. Some Criminals will continue to repent, and overall the status quo will remain until the next time this is brought to court.
http://www.catholicnewsagency.com/news/ ... ase-53807/
http://www.catholicherald.co.uk/news/20 ... onal-seal/
http://www.tri-parishtimes.com/opinion/ ... f887a.html
http://www.catholicsentinel.org/main.as ... leID=26394
http://douthat.blogs.nytimes.com/2014/0 ... se-tangle/
https://time.com/3318814/catholic-confe ... fidential/
http://www.patheos.com/blogs/thejesuitp ... nviolable/