Matthew 15:10-20 (ESV)
“ And he called the people to him and said to them, "Hear and understand:  it is not what goes into the mouth that defiles a person, but what comes out of the mouth; this defiles a person."  Then the disciples came and said to him, "Do you know that the Pharisees were offended when they heard this saying?"  He answered, "Every plant that my heavenly Father has not planted will be rooted up.  Let them alone; they are blind guides. And if the blind lead the blind, both will fall into a pit."  But Peter said to him, "Explain the parable to us."  And he said, "Are you also still without understanding?  Do you not see that whatever goes into the mouth passes into the stomach and is expelled?  But what comes out of the mouth proceeds from the heart, and this defiles a person.  For out of the heart come evil thoughts, murder, adultery, sexual immorality, theft, false witness, slander.  These are what defile a person. But to eat with unwashed hands does not defile anyone."
“Do you know that the Pharisees were offended when they heard this saying?” Jesus all but tells them get used to it. leave them alone they are blind guides. The gospel so often offends. It is so contrary to what we normally believe about ourselves. We like to think that our hearts are filled with all sorts of nice things. We like to think that what matters is the out ward things, what we eat and drink, whether or not we wash our hands. Jesus turns it all on its head. It is what comes out of the mouth that defiles a person, not what goes in.
Here Jesus has in mind the false teachings of Pharisees, much more than he has something like cussing in mind. Even in these things Christians often seem to be a bit confused. No one bats an eye at OMG, but drop an F-bomb and see what happens. I suppose one need not needlessly offend with things like this, but then sometimes you wonder what right a person has to be offended at it in the first place. It may just be another way in which the reality is we replace God’s law with our own. The Bible itself uses some pretty obscene, course, and foul language in the original languages of Greek and Hebrew, though perhaps a bit more sparingly than Martin Luther.
And then no one is at all offended when Baptists challenge a person’s baptism and refuse children the grace of God, teaching them to despise baptism. In truth they do offend in the worst manner, they scandalize and cause to stumble these little ones as they point them away from Christ and his promises and to themselves their own works and repentance. But not true repentance just a feeling sorry for actual sins. In a weird way Baptists say you need to repent, and then they conceive of this repentance as a ceasing to do particular sins, sexual immorality, perhaps drinking and smoking. But you can’t repent of these unless you do them. So in a weird way, you actually have to sin, before you can be saved! Well the truth is we all are sinners to begin with, but at least we don’t have to be guilty of sexual immorality before we can be saved. We can just break that first commandment by not having faith in the Triune God, and then repent by believing and being baptized which two things cannot be properly separated. I’ve digressed.
These are blind guides, leave them alone, let them be scandalized as it were by the gospel. You still have to give it to them, and share it with their people. If they want to be offended just let them be, shake the dust from your feet.