http://www.clerus.org/clerus/dati/2001-03/22-13/1L.html
So according to GNicodemus Satan realizes that Jesus is merely a man (and not the Son of God) because of this episode in Mark 14:
Note that Jesus is invoking two deities, and not one: the god of the Jews named Abbà and a higher god, the unknown Father adored by Marcion and the gnostics. Really, under a separationist view of Mark, the mere man Jesus invokes YHWH while the divine Christ (possessing Jesus) invokes his unknown Father.
By seeing the scene, Satan is moved to think (wrongly) that YHWH/Abbà = the Father. Hence, Jesus had to be for him only a mere man "of the race of the Jews".
So by introducing Barabbas as a parody of the gnostic Son of Father, the judaizing interpolator is identifying the Father with Abbà so there are no doubts that the gnostic "Son of Father" was not the crucified Christ insofar Abbà means Father.
I wonder if there is some suggestive Gnostic relation between “Abba, Father” and the choice between Jesus and Barabbas. I try.
Just as Satan thinks that the mere man Jesus who invokes Abbà coincides with the same person who invokes the Father, so the Jews are moved to believe that the Christ is the mere man named Jesus and not rather Jesus Barabbas aka the gnostic "Jesus the Son of the Father": in this sense Jesus Barabbas is the real Christ who remained impassible while the mere man Jesus was crucified in his place.