As Celsus supposes that we uphold the doctrine of the resurrection in order that we may see and know God, he thus follows out his notions on the subject: “After they have been utterly refuted and vanquished, they still, as if regardless of all objections, come back again to the same question, 'How then shall we see and know God? How shall we go to Him?'” Let any, however, who are disposed to hear us observe, that if we have need of a body for other purposes, as for occupying a material locality to which this body must be adapted, and if on that account the “tabernacle” is clothed in the way we have shown, we have no need of a body in order to know God.
For that which sees God is not the eye of the body; it is the mind which is made in the image of the Creator, and which God has in His providence rendered capable of that knowledge. To see God belongs to the pure heart, out of which no longer proceed “evil thoughts, murders, adulteries, fornications, thefts, false witness, blasphemies, the evil eye,” or any other evil thing. Wherefore it is said, “Blessed are the pure in heart, for they shall see God.” But as the strength of our will is not sufficient to procure the perfectly pure heart, and as we need that God should create it, he therefore who prays as he ought, offers this petition to God, “Create in me a clean heart, O God.”
Source: Against Celsus (New Advent)