Our problem is not the lack of a Biblical mandate. Internationals are our modern-day Samaritans. Our problem is not lack of resources either. Though it makes a lot of sense to empower people to reach internationals, we keep treating internationals as virtually invisible. Part of the answer may lie on our own ethnocentrism.
Unchecked ethnocentrism leads to a lack of love.
Lack of love is bad news for the Gospel. You have to realize you are asking them to love the same people who are breaking into their houses and raping their daughters. This statement is factually wrong and theologically unsound. Several years ago I was candidating at a church located in a highly diverse neighborhood. The senior pastor was doing his best to try to convince me that his people did not see color or ethnicity.