1 Vain, too, is [the effort of] Marcion and his followers when they [seek to] exclude Abraham from the inheritance, to whom the Spirit through many men, and now by Paul, bears witness, that “he believed God, and it was imputed unto him for righteousness.” And the Lord [also bears witness to him,] in the first place, indeed, by raising up children to him from the stones, and making his seed as the stars of heaven, saying, “They shall come from the east and from the west, from the north and from the south, and shall recline with Abraham, and Isaac, and Jacob in the kingdom of heaven;” and then again by saying to the Jews, “When you shall see Abraham, and Isaac, and Jacob, and all the prophets in the kingdom of heaven, but you yourselves cast out.” This, then, is a clear point, that those who disallow his salvation, and frame the idea of another God besides Him who made the promise to Abraham, are outside the kingdom of God, and are disinherited from [the gift of] incorruption, setting at naught and blaspheming God, who introduces, through Jesus Christ, Abraham to the kingdom of heaven, and his seed, that is, the Church, upon which also is conferred the adoption and the inheritance promised to Abraham.
2. For the Lord vindicated Abraham's posterity by loosing them from bondage and calling them to salvation, as He did in the case of the woman whom He healed, saying openly to those who had not faith like Abraham, “You hypocrites, does not each one of you on the Sabbath-days loose his ox or his ass, and lead him away to watering? And ought not this woman, being a daughter of Abraham, whom Satan has bound these eighteen years, be loosed from this bond on the Sabbath-days?” It is clear therefore, that He loosed and vivified those who believe in Him as Abraham did, doing nothing contrary to the law when He healed upon the Sabbath day. For the law did not prohibit men from being healed upon the Sabbaths; [on the contrary,] it even circumcised them upon that day, and gave command that the offices should be performed by the priests for the people; yea, it did not disallow the healing even of dumb animals. Both at Siloam and on frequent subsequent occasions, did He perform cures upon the Sabbath; and for this reason many used to resort to Him on the Sabbath-days. For the law commanded them to abstain from every servile work, that is, from all grasping after wealth which is procured by trading and by other worldly business; but it exhorted them to attend to the exercises of the soul, which consist in reflection, and to addresses of a beneficial kind for their neighbours' benefit. And therefore the Lord reproved those who unjustly blamed Him for having healed upon the Sabbath-days. For He did not make void, but fulfilled the law, by performing the offices of the high priest, propitiating God for men, and cleansing the lepers, healing the sick, and Himself suffering death, that exiled man might go forth from condemnation, and might return without fear to his own inheritance.
3. And again, the law did not forbid those who were hungry on the Sabbath-days to take food lying ready at hand: it did, however, forbid them to reap and to gather into the barn. And therefore did the Lord say to those who were blaming His disciples because they plucked and ate the ears of grain, rubbing them in their hands, “Have you not read this, what David did, when himself was an hungered; how he went into the house of God, and ate the show-bread, and gave to those who were with him; which it is not lawful to eat, but for the priests alone?” justifying His disciples by the words of the law, and pointing out that it was lawful for the priests to act freely. For David had been appointed a priest by God, although Saul persecuted him. For all the righteous possess the sacerdotal rank. And all the apostles of the Lord are priests, who do inherit here neither lands nor houses, but serve God and the altar continually. Of whom Moses also says in Deuteronomy, when blessing Levi, “Who said unto his father and to his mother, I have not known you; neither did he acknowledge his brethren, and he disinherited his own sons: he kept Your commandments, and observed Your covenant.” But who are they that have left father and mother, and have said adieu to all their neighbours, on account of the word of God and His covenant, unless the disciples of the Lord? Of whom again Moses says, “They shall have no inheritance, for the Lord Himself is their inheritance.” And again, “The priests the Levites shall have no part in the whole tribe of Levi, nor substance with Israel; their substance is the offerings (fructifications) of the Lord: these shall they eat.” Wherefore also Paul says, “I do not seek after a gift, but I seek after fruit.” To His disciples He said, who had a priesthood of the Lord, to whom it was lawful when hungry to eat the ears of grain, “For the workman is worthy of his meat.” And the priests in the temple profaned the Sabbath, and were blameless. Wherefore, then, were they blameless? Because when in the temple they were not engaged in secular affairs, but in the service of the Lord, fulfilling the law, but not going beyond it, as that man did, who of his own accord carried dry wood into the camp of God, and was justly stoned to death. “For every tree that brings not forth good fruit shall be hewn down, and cast into the fire;” and “whosoever shall defile the temple of God, him shall God defile.”
Source: Adversus haereses (New Advent)