'Impurities' in the Bible

"The land you are entering to possess is a morally unclean land due to the moral uncleanness of the nations of the lands along with their abominations that has filled it from one end to the other with their impurities. So, therefore, do not give your daughters in marriage to their sons, nor marry their daughters to your sons, and under no circumstances are you to seek their well-being or their wealth, so that you may remain strong, enjoying the best things the land has to give, and so that you may establish an inheritance for your children forever.'