Christ must reign. The ‘must’ is very emphatic in the original Greek.
All the victories that Christ gains will be given to his people. They too will trample Satan under their feet, and to his eternal shame the weak will prevail over the strong (Romans 16:20). The saints will receive immortality and like Christ will rise to die no more, for death will no longer have power over them (Romans 6:9-11). They will put on immortality (1 Corinthians 15:53-54; 2 Timothy 1:10).