The Book of Revelation says Two Witnesses will arrive on the scene during the end time just before the second coming of Jesus Christ.  They will carry out with great power a three and half year's ministry, warning of the soon coming Day of the Lord and fighting evil led by Satan.  We don't know exactly who the Two Witnesses are, but people have debated it for decades.  Some say they will be Elijah and Enoch, others believe it could be Elijah and Moses, some think it will be other people, finally others think they are not just two people but rather a representation of many Christians.  A very interesting story that I look at in this video "Who Are The Two Witnesses In Revelation?"