NOW we know Him by the Spirit. Not in things we can SEE, HEAR, SMELL, TASTE, or TOUCH.
here's the entire passge:
[15] And Christ died for all; that they also who live, may not now live to themselves, but unto him who died for them, and rose again. [16] Wherefore henceforth, we know no man according to the flesh. And if we have known Christ according to the flesh; but now we know him so no longer. [17] If then any be in Christ a new creature, the old things are passed away, behold all things are made new. [18] But all things are of God, who hath reconciled us to himself by Christ; and hath given to us the ministry of reconciliation. [19] For God indeed was in Christ, reconciling the world to himself, not imputing to them their sins; and he hath placed in us the word of reconciliation. [20] For Christ therefore we are ambassadors, God as it were exhorting by us. For Christ, we beseech you, be reconciled to God.
What St. Paul is talking about is the spiritual nature of a Catholic Christian man, which exceeds considerations of carnal nature, familiy ties, ethnic kinship and so forth. He is not saying that Christians should abandon their sense of vision, hearing, etc. but rather that their material life has been sanctified in Christ: "behold all things are made new", and continues to be sanctified through the ministry of confession, which St. Paul calls "reconciliation".