Jesus said, "If your leaders say to you, 'Look, the Kingdom is in the sky,' then the birds of the sky will precede you. If they say to you, 'It is in the sea,' then the fish will precede you. Rather, the Kingdom is within you and it is outside you.
When you know yourselves, then you will be known, and you will understand that you are children of the living Father. But if you do not know yourselves, then you live in poverty, and you are the poverty."-Gospel of Thomas
William Blake, Christ in the House of Martha and Mary.
The Kingdom is a symbol for the Self, which Jesus exhorts us to know. It is coextensive with the Universe, and therefore both inside and outside us.