Verse: Matthew 7:6
6 “Do not give dogs what is sacred; do not throw your pearls to pigs. If you do, they may trample them under their feet, and turn and tear you to pieces.
Ok, I am no bible scholar. I've read some commentary on this verse and there doesn't seem to be total agreement on what this exactly means. Some think that it ties into the verses above it about judgment and the plank and the speck. The thought is that Jesus is saying, don't offer the pearls of Christian community to people who are judgmental and hypocritical. They are not submitted to the Lord, and our efforts to share community with them may end up biting us. Maybe we need to use discernment as to who we open our lives to and even whom we invite into deep Christian community. If they are unsafe, out to destroy us or the church, have hidden agendas, or are wolves in sheep's clothing, it may be best to not offer the depths of Christian community to them.
Many others interpret it to be talking about people who are hostile to the Gospel—that we shouldn't go preaching to people who don't want to hear it. And not because we are mad at them or we don't love them. It's more like this: there is a time and a place when someone will be receptive to the Gospel message, so maybe we need to use discernment and not just throw out the pearls of the Gospel when we know they aren't ready to hear them. Maybe forcing that on them at the wrong time will have the opposite effect—rather than them coming to know Jesus, they will turn and "tear you to pieces."
The common theme between those two possible interpretations is discernment. Whether it is choosing to open our hearts to people or share the Gospel with people, it is OK and right for us to use God's discernment. There are people we should have boundaries with. It is OK to use discernment if we sense someone is "off" or has "ill will" towards us or our church. There are still ways to love them without "casting our pearls" before them. Similarly, it is OK to use discernment when sharing the Gospel with those who don't believe. Sharing the Gospel is not a "one size fits all" strategy. With some people it might be right and good to share the Gospel using words right away. With others, that could actually end up backfiring. Some need us to just love them and show them the Gospel first. Some just need us to pray and wait.
If you are anything like me you like answers that make sense. A+B=C. But life and faith aren't always like that. And some of what we do as Christians is learn to live in the mystery of faith, all the while trusting Jesus and being led by this Holy Spirit. Remember he said to us that his Spirit would lead us into all truth. So we can learn to depend on the Spirit in these situations (and on the wisdom of other believers) to help us find this discernment.