Tertullian

For what are this next words? "Now this I say, brethren, that flesh and blood cannot inherit the kingdom of God." He means the works of the flesh and blood, which, in his Epistle to the Galatians, deprive men of the kingdom of God.

Now if, on the contrary, there is to be no flesh, how then shall it put on incorruption and immortality? Having then become something else by its change, it will obtain the kingdom of God, no longer the (old) flesh and blood, but the body which God shall have given it. Rightly then does the apostle declare, "Flesh and blood cannot inherit the kingdom of God; " for this (honour) does he ascribe to the changed condition which ensues on the resurrection.

When also he (in a later passage) enjoins us "to cleanse ourselves from all filthiness of flesh and blood" (since this substance enters not the kingdom of Gods ); when, again, he "espouses the church as a chaste virgin to Christ," a spouse to a spouse in very deed, an image cannot be combined and compared with what is opposed to the real nature the thing (with which it is compared).

The apostle, however, himself here comes to our aid; for, while explaining in what sense he would not have us "live in the flesh," although in the flesh-even by not living in the works of the flesh -he shows that when he wrote the words, "Flesh and blood cannot inherit the kingdom of God," it was not with the view of condemning the substance (of the flesh), but the works thereof; and because it is possible for these not to be committed by us whilst we are still in the flesh, they will therefore be properly chargeable, not on the substance of the flesh, but on its conduct.