One knows Jesus lives because they have personally encountered him. They have walked with him in life as Enoch walked with God. They aren’t living off another’s life experience and stories. Instead their life is filled with their own miraculous stories about when God caused them to walk in faith, when God rescued them, when God revealed himself to them in ways no one else could see but their own eyes. They know what they have seen with their own eyes, heard with their own ears concerning the Word of life. The life was made manifest to them. (1 John 1:1-3) They may not have touched Christ as John and the other apostles did but they cannot deny that Christ has touched them and spoken to them.  They may not be able to understand it fully or explain it, but they know Christ yet lives because God has revealed Him to them in their own lives.