Dick writes Claudia on the vernal equinox and tells her not only is it spring but it is also the Springtime the entity told him would eventually arrive. The tyranny, he thinks, has ended.
His conception of the universe (at least for now) is a cube. We are all inside this cube and the patterns are fed to us. He uses Beethoven as an example of how signals are passed to humans for us to uniquely modify to produce an output. Another way to look at life is as a barrel that we roll up a hill until we eventually reach God… not the clearest metaphor here.
Dick ends the letter by briefly recounting what happened to him in 1974.
March 16, 1974: The entity appeared to him.
March 18, 1974: The entity looked out from inside him and denied the reality of the world.
March 20, 1974: The entity took over, showing him what was real.
March 20 until late July, 1974: The entity showed him how to defeat the world’s tyrannies.
August 1974 and on: The entity (aka Elijah/the Holy Spirit/Dionysus/Zagreus) gradually went away leaving him mentally healed.