Exodus 23:33 "They shall not dwell in your land lest they make you sin against Me"

We are not allowed to allow idol-worshipers to live in Eretz Yisrael to make sure that we will not be influenced by their belief.

However, if an idol-worshiper renounces his belief and no longer practices his religion, we may allow him to stay in Eretz Yisrael. Such an individual is called a "Ger Toshav".