What does Mark 13:10 mean?

Mark is the only Gospel author to record this quote, which has puzzled scholars for generations. "Nations" is from the Greek root word ethnos. It means any group of people that is affiliated in some way, whether by geography, culture, or tribe. Preterists and semi-preterists believe that end-times prophecy is not literal, and understand "nation" to mean the people groups within the Roman Empire, a much more reasonable goal, or the nations known to the people of Judea in this moment. The work of missionaries in the last hundred years proves that we do not have to interpret this verse so conservatively.

If the verse means the end times will not come until the gospel spreads to every people group on earth, we are almost there. According to the Bible translation ministry Wycliffe, the Bible has been at least partially translated into 3312 out of the 7099 languages currently known to be in use. The complete Bible has been translated in 670 languages and the New Testament in 1521. As of this writing, BibleRef.com's parent ministry, GotQuestions.org, has gospel presentation pages translated into 167 languages. Over eighty percent of the world has internet access, and that number is quickly rising with the spread of smartphones. Statisticians suggest that ninety percent of online users can be reached using only twenty-one languages.

We may never arrive at the place where every single person has heard the gospel. However, we are rapidly reaching the point where someone from every tribe will.