The fish symbol, the ichthus, was one of the earliest symbols representing Jesus Christ. The word in Greek, ΙΧΘΥΣ, is an acronym for Ἰησοῦς Χριστός Θεοῦ Υἱός Σωτήρ — Iēsous Christos Theou Uios Sōtēr – translated into English as Jesus Christ, Son of God, Savior. Jesus is the fish, and the fish was used as a sign in which Christians could identify each other.
Theologically, Christians found great significance to the fact that Jesus can be represented by a fish. Not only were many of his Apostles, including the leader of the Apostles, a fisherman who can be said to have found the one true fish, the fish sign connects Jesus to baptism. Optatus writing against the Donatists brings this out:
But I do not know if it came with that fish, which is understood as Christ, which in recitation of the patriarchal narratives is said to have been caught in the Tigris, whose gall-bladder and liver Tobias took to guard the woman Sara and to bring light to the blindness of Tobias; by the insides of the same fish the demon Asmodeus was driven away from the girl Sara, who is understood as the church, and blindness was expelled from Tobias. This is the fish, which in baptism is introduced into the waves of the font, so that what was water may also be called a fishpool because of the fish. The name of this fish according to its Greek appellation IKTHUS contains a host of holy names in its individual letters, being in Latin Jesus Christ Son of God Saviour. This fishpool, which in the whole catholic church throughout the world abounded with saving waters for the life of the human race, you translated to serve your own will, and you dissolved the single baptism, by which walls are made to guard human beings, and you made, as it were, other walls, but no good building. 
While Jesus is himself represented by the sign of the fish, Christians themselves also become fish in Christ. Jesus, summoning Peter and Andrew to do his work, said, “Follow me, and I will make you fishers of men” (Matt 4:19 RSV). Humans are to become fish, caught up by the Apostles. This happens, of course, as they are incorporated into Christ. In baptism, they die to themselves and arise in Christ, arise in Jesus the fish. “For as many of you as were baptized into Christ have put on Christ” (Gal 3:27 RSV). And in communion, they are fed the fish, the fish which is miraculously multiplied so as to feed the multitude. In communion, in partaking of the fish, they realize their baptism; they merge with the fish, making it a part of them as they become a part of it – they become, through such incorporative adoption, a child of God.
Fish have no need for guns. They can’t hold them. But this is not to say fish have no way of resisting evil in the world. Their way, cannot be the way of the world but the way of Jesus the true fish. Their merging with Christ allows them to have victory over the world through the accomplishment and action of Christ. The city of the devil, the black iron prison, might appear to be in control, for it seems to have had a victory over Christ by turning Christians against the teachings of their Lord, but the reality is quite different. No matter what the empire might do, Christ overcomes through his self-sacrifice. The apparent victory of evil, as seen by the brutal assault of the powers of darkness against Christ on the cross, reveals the real victory of the good, and provides the means by which the good is able to spread throughout the world and incorporate itself into the hearts of the multitude.
It was through the sign of the fish that Philip K. Dick himself felt drawn to Christ, and was able to appreciate the great victory of Christ. Seeing a woman wearing an ichthus, his awareness toward Christ changed, and he felt as if he had an anamnesis, an awakening of his mind. Everything changed for him. His attempt to understand the world and its history could not be done without the sign of the fish, without a recognition of Christ. He did not know how to interpret Christ – he was cynical of traditional Christianity – but he also knew he could not deny the position Christ held in universal history. He asked himself again and again – what is it that enslaves us, what is the black iron prison? What did Christ’s work accomplish in relation to the black iron prison? Who won? Who lost? In thinking this through it would be the sign of the fish which would give him his answer:
Q: Who won? Christianity or the Empire?
A: Ostensibly, Christianity won, but covertly underneath the Empire won.
Q. You are wrong. Underneath the Empire lies the secret victory of the Fish: true Christianity.
How is this so? On the one hand, the world seems to show that Christianity was victorious, and so overcame the darkness of the Empire. But then Christendom slowly found itself following the path of the Empire itself. It became brutal, it did to its opponents what the Empire did to Christians. The Empire, then, is in control. But is it? The answer is all in the fish:
These are not temporal or spatial layers but ontological layers. The least real is the ostensible victory of Christianity over the Empire; under it, more real, is the Empire victory, which is deliberately concealed, and no one realizes it, eine Geheimnis. But most real of all, is the innermost layer of victory by the fish which means fish teeth: viz.: The fish fights back. But, paradoxically, the fish fights back by being sliced up by the metal teeth (i.e., the Empire); it feeds the faithful when the Empire cuts it up.
Yes, the empire in cutting up the fish, in killing Christ on the cross, the empire acts according to its innermost values. Its cruelty is exposed. It imprisons, it enslaves, it cuts up and destroys anyone who gets in its way. But Christ does something unique here – by giving the empire what it wants, by giving it an apparent victory, it plays into Christ’s hands and lets him expose the violent core and to overcome in in himself. He is cut up, he is fed to his followers, he turns them into fish, all the while he himself rises up victorious and takes with him all those who have become fish like him. The empire’s victory is its own defeat. Christ’s defeat is his victory. The inner nature of the world shows Christ feeding all those who the empire has brutalized. He grants them himself, so that they can find the true life, the life which can only be had in Christ the fish And once this recognize this overthrow of the path of violence, the way of empire, they too will know, really know, fish have no need for guns. They will live forever in the water of life, the kingdom of heaven, the peaceable kingdom of God.