Adam, then, was the source of both cities--the one headed by Cain and his descendants (who have only a very limited family tree in Scripture, symbolizing their dedication to earthly peace and ownership of the passing world. The other headed by Abel and Seth, focused on the heavenly things, persecuted by the earthly city, and founded by "resurrection" of the soul by the hand of God. ("Seth," Augustine says, means "resurrection.")
In Abel, Seth, Enos, and Enoch, we see types of those who are brought into the Heavenly City by "the election of grace".
Consequently no one ought to trust in himself that he shall become a citizen of that other city which is not dedicated in the name of Cain’s son in this present time, that is to say, in the fleeting course of this mortal world, but in the immortality of perpetual blessedness.That is, we must not look to ourselves for the reason we are in the City of God--that is the nature of Cain's city. Instead, we must look to God Himself as the source of our salvation. This salvation will one day be fulfilled by our translation from this earthly city into the heavenly one, just as Enoch typified.