In my humble opinion, Heinlein's last writings were exploring mortality. Here's the list of those "last writings" I consider variations on this theme:
- 1966, The Moon is a Harsh Mistress
- 1970, I Will Fear No Evil
- 1973, Time Enough for Love
- 1980, The Number of the Beast
- 1982, Friday
- 1984, Job: A Comedy of Justice
- 1985, The Cat Who Walks Through Walls
- 1987, To Sail Beyond the Sunset
Look at the various ways in which he explored the possibility of immortality: a sentient computer, brain transplant into a new body, longevity genes and treatments (Lazarus Long), cloning/engineered genetics.
I have read everything he wrote. Having just finished a re-read of
Stranger in a Strange land, I'm chomping at the bit to go back and re-read all of his books. (Problem is that there are so many books I haven't read even once!) One of my very favorites is
The Moon is a Harsh Mistress and I'm going to definitely put this one at the top of my list.