People need to hear the Gospel. It is imperative that we do all we can to tell others the good news of Jesus Christ. The Bible commands believers everywhere to love their neighbors, serve others, extend kindness, be ambassadors of peace and so much more. This is a vital need in our world today. When we invite others to know Jesus, we are living like Christ and shining his light into dark places.
There are countless individuals and people groups around the world who do not know Jesus. Mission work is necessary in order to engage people from a different culture. This is accomplished by learning the culture, preaching the gospel and raising up Christian leaders within said culture to do the same.