my true yokefellow (or loyal Syzygus): The Greek word suzuge is either a personal name or a description. We do not know exactly who this person was.
Nothing more is known about Clement.
whose names are in the Book of Life: Those whose names are written in the Book of Life are true believers. God will give them eternal life (see Luke 10:20; Revelation 3:5; 13:8; 17:8; 20:12, 15; 21:27; compare Exodus 32:32; Psalm 69:28; Daniel 12:1).