Boundaries help us to distinguish our property so that we can take care of it. They help us to "guard our heart with all diligence." We need to keep things that will nurture us inside our fences and keep things that will harm us outside. In short, boundaries help us keep the good in and the bad out. They guard our treasures (Matt. 7:6) so that people will not steal them. They keep the pearls inside, and the pigs outside.
Sometimes, we have bad on the inside and good on the outside. In these instances, we need to be able to open up our boundaries to let the good in and the bad out. In other words, our fences need gates in them. For example, if I find that I have some pain or sin within, I need to open up and communicate it to God and others, so that I can be healed. Confessing pain and sin helps to "get it out" so that it does not continue to poison me on the inside (1 John 1:9; James 5:16; Mark 7:21 - 23).
And when the good is on the outside, we need to open our gates and "let it in." Jesus speaks of this phenomenon in "receiving" him and his truth (Rev. 3:20; John 1:12). Other people have good things to give us, and we need to "open up to them" (2 Cor. 6:11 - 13). Often we will close our boundaries to good things from others, staying in a state of deprivation.
In short, boundaries are not walls. The Bible does not say that we are to be "walled off" from others; in fact, it says that we are to be "one" with them (see John 17:11). We are to be in community with them. But in every community, all members have their own space and property. The important thing is that property lines be permeable enough to allow passing and strong enough to keep out danger.
Often, when people are abused while growing up, they reverse the function of boundaries and keep the bad in and the good out. When Mary was growing up she suffered abuse from her father. She was not encouraged to develop good boundaries. As a result, she would close herself off, holding the pain inside; she would not open up to express her hurt and get it out of her soul. She also would not open up to let support from the outside in to heal her. In addition, she would continually allow others to "dump" more pain into her soul. Consequently, when she came in for help, she was carrying a lot of pain, still being abused, and "walled off" from support from the outside.
She had to reverse the ways her boundaries worked. She needed fences that were strong enough to keep the bad out and gates in those fences to let out the bad already in her soul and let in the good she desperately needed.