Should there be a difference between the character portrayed and the actor's true personality?

It depends, if the acting that they are doing affects their personal lives and thier walk with Christ, then they should not play the role of the character who is doing these unChrist-like things. If the character is genuinely in a true relationship with God, they should be completely seperate in terms of personality between their character and thier true self. If they do not endorse the things that they do in the movie, and do not let it affect them, then they will be fine. An example to prove this is in a school play. If a character is portraying actions that are not congruent with their faith, and they do not mean the lines that they say, it is simply acting. Acting is portraying a part to most reflect the character, not ourselves. This is why the people who act in a movie generally refer to themselves in third person as "the character" because they are not trying to be themselves. The goal of acting is to give someone who has skill in understanding the personality of the implied character, and being able to mimic their actions and attitudes on screen for an audience. It brings art and aesthetic value to the media presented. It does something that most people cannot do. I say that if a Christian swears in a movie, and doesn't promote it, it is actually worthwile in presenting a part.