The plot is similar to the Original Series episode “The Way to Eden” with some elements reminiscent of “Who Mourns for Adonais?” Shatner probably had the concepts of these episodes in mind (at least subconsciously) and took them a few steps further based on his fascination with televangelists. The Motion Picture did the same thing with “The Changeling."
shareyes. also elements of Where No Man Has Gone Before (the barrier, crazed God like being)
and in addition to Changeling TMP had elements of Corbomite. Immunity Syndrome, Doomsday Machine.
Good parallels.
ST:TMP also brings to mind “Metamorphosis," which is a mature and serious Trek drama where Kirk, Spock and McCoy encounter the unknown in space and have to deal with it. The Motion Picture often has the same vibe; neither story contains much action. And the way Zefram Cochrane communes with The Companion in “Metamorphosis” brings to mind the way Decker ultimately merges with V’ger in ST:TMP.
Also, the android Ilia-probe is reminiscent of the androids in “What Are Little Girls Made of?," “I, Mudd” and “Requiem for Methuselah.”