1 And inasmuch as the apostle has not pronounced against the very substance of flesh and blood, that it cannot inherit the kingdom of God, the same apostle has everywhere adopted the term “flesh and blood” with regard to the Lord Jesus Christ, partly indeed to establish His human nature (for He did Himself speak of Himself as the Son of man), and partly that He might confirm the salvation of our flesh. For if the flesh were not in a position to be saved, the Word of God would in no wise have become flesh. And if the blood of the righteous were not to be inquired after, the Lord would certainly not have had blood [in His composition]. But inasmuch as blood cries out (vocalis est) from the beginning [of the world], God said to Cain, when he had slain his brother, “The voice of your brother's blood cries to Me.” And as their blood will be inquired after, He said to those with Noah, “For your blood of your souls will I require, [even] from the hand of all beasts;” and again, “Whosoever will shed man's blood, it shall be shed for his blood.” In like manner, too, did the Lord say to those who should afterwards shed His blood, “All righteous blood shall be required which is shed upon the earth, from the blood of righteous Abel to the blood of Zacharias the son of Barachias, whom you slew between the temple and the altar. Verily I say unto you, All these things shall come upon this generation.” He thus points out the recapitulation that should take place in his own person of the effusion of blood from the beginning, of all the righteous men and of the prophets, and that by means of Himself there should be a requisition of their blood. Now this [blood] could not be required unless it also had the capability of being saved; nor would the Lord have summed up these things in Himself, unless He had Himself been made flesh and blood after the way of the original formation [of man], saving in his own person at the end that which had in the beginning perished in Adam.
2. But if the Lord became incarnate for any other order of things, and took flesh of any other substance, He has not then summed up human nature in His own person, nor in that case can He be termed flesh. For flesh has been truly made [to consist in] a transmission of that thing moulded originally from the dust. But if it had been necessary for Him to draw the material [of His body] from another substance, the Father would at the beginning have moulded the material [of flesh] from a different substance [than from what He actually did]. But now the case stands thus, that the Word has saved that which really was [created, viz.,] humanity which had perished, effecting by means of Himself that communion which should be held with it, and seeking out its salvation. But the thing which had perished possessed flesh and blood. For the Lord, taking dust from the earth, moulded man; and it was upon his behalf that all the dispensation of the Lord's advent took place. He had Himself, therefore, flesh and blood, recapitulating in Himself not a certain other, but that original handiwork of the Father, seeking out that thing which had perished. And for this cause the apostle, in the Epistle to the Colossians, says, “And though you were formerly alienated, and enemies to His knowledge by evil works, yet now you have been reconciled in the body of His flesh, through His death, to present yourselves holy and chaste, and without fault in His sight.” He says, “You have been reconciled in the body of His flesh,” because the righteous flesh has reconciled that flesh which was being kept under bondage in sin, and brought it into friendship with God.
3. If, then, any one allege that in this respect the flesh of the Lord was different from ours, because it indeed did not commit sin, neither was deceit found in His soul, while we, on the other hand, are sinners, he says what is the fact. But if he pretends that the, Lord possessed another substance of flesh, the sayings respecting reconciliation will not agree with that man. For that thing is reconciled which had formerly been in enmity. Now, if the Lord had taken flesh from another substance, He would not, by so doing, have reconciled that one to God which had become inimical through transgression. But now, by means of communion with Himself, the Lord has reconciled man to God the Father, in reconciling us to Himself by the body of His own flesh, and redeeming us by His own blood, as the apostle says to the Ephesians, “In whom we have redemption through His blood, the remission of sins;” and again to the same he says, “You who formerly were far off have been brought near in the blood of Christ;” and again, “Abolishing in His flesh the enmities, [even] the law of commandments [contained] in ordinances.” And in every Epistle the apostle plainly testifies, that through the flesh of our Lord, and through His blood, we have been saved.
4. If, therefore, flesh and blood are the things which procure for us life, it has not been declared of flesh and blood, in the literal meaning (proprie) of the terms, that they cannot inherit the kingdom of God; but [these words apply] to those carnal deeds already mentioned, which, perverting man to sin, deprive him of life. And for this reason he says, in the Epistle to the Romans: “Let not sin, therefore, reign in your mortal body, to be under its control: neither yield your members instruments of unrighteousness unto sin; but yield yourselves to God, as being alive from the dead, and your members as instruments of righteousness unto God.” In these same members, therefore, in which we used to serve sin, and bring forth fruit unto death, does He wish us to [be obedient] unto righteousness, that we may bring forth fruit unto life. Remember, therefore, my beloved friend, that you have been redeemed by the flesh of our Lord, re-established by His blood; and “holding the Head, from which the whole body of the Church, having been fitted together, takes increase” — that is, acknowledging the advent in the flesh of the Son of God, and [His] divinity (deum), and looking forward with constancy to His human nature (hominem), availing yourself also of these proofs drawn from Scripture— you easily overthrow, as I have pointed out, all those notions of the heretics which were concocted afterwards.
Source: Adversus haereses (New Advent)