For many Christians (mostly Protestants) salvation is determined by faith alone, not works (deeds). That type of salvation is known as sola fide. The concept is derived form Ephesians 2:8-9...
For it is by grace you have been saved, through faith—and this is not from yourselves, it is the gift of God— not by works, so that no one can boast.
The problem is that many Christians cherry pick this verse and ignore what the rest of the Bible says, especially Revelation 20:12...
And I saw the dead, the great and the small, standing before the throne, and books were opened; and another book was opened, which is the book of life; and the dead were judged from the things which were written in the books, according to their deeds.
And James 2:26...
For just as the body without the spirit is dead, so also faith without works is dead.
It would seem that it takes just more than a belief in order to pass judgment and make it to paradise. You must walk the walk, not just talk the talk. That's why you can't just do anything you want to as long as you are "saved." It would seem that the Catholics and Eastern Orthodox are right on this point, within the realm of Christianity.