Nature teaches us that in order for life to thrive the most important parts must be protected from the outside environment. The most basic border surrounds every human being and that is skin. Skin protects your body from dramatic temperature changes, pathogens, and maintains your fluids. Remove the border in the wrong areas and you are subject to death.
Of course there must be openings in the border to maintain life as well. You have the mouth opening so that important resources for the body may enter, but care must be taken on what enters otherwise death again can occur. Borders are necessary and discrimination is necessary so that the body receives what it requires at the same time, preventing what is not required.
A successful nation, a successful church must act like the body or it will fail to exist. Borders are necessary for the cells (people) inside the body to flourish. If borders (skin) is not maintained and/or repaired if broken, your body, your church, your nation will fall. It is Biblical wisdom to protect the house by setting up borders to protect yourself from sin.