"In the canonical Gospels, the 'kingdom of God' is his reign; God remakes this world in conformity with his own plan-hence, the Lord's prayer: 'Your kingdom come, your will be done, on earth as it is in heaven' (Matthew 6:10; cf. Luke 11:2). God's kingdom is his perfect will, coming to pass here specifically in the Gospels through Jesus' reign as God's messianic king. It is very much something that comes from outside, from God himself, to human beings through Jesus' ministry. In the Gospel of Thomas, however the picture is quite different: The kingdom is something that dwells in elect disciples, a kind of 'true soul'...Some of the details are vague, because the Gospel of Thomas is a collection of often enigmatic sayings, but is tolerably clear that this is true soul is what needs to escape from this woeful world and from the physical body which binds the soul in the present...In the midst of these controversies that characterized early Christianity, Thomas proposes a radical vision of an un-Jewish Jesus and of a rejection of the world and the body in favor of a focus on rigorous training of the soul to enable its escape to re-enter the divine."
This is not far from some interpretations of the "kingdom" today: "Earth bad, heaven good. Body bad, outside the body in an ethereal, nebulous existence-good." This, however, is not Jesus' gospel of the kingdom of God/heaven message.