He also makes the observance of the decalogue the test of true piety. Thus he says:--
"They (the Jews) had therefore a law, a course of discipline, and a prophecy of future things. For God at the first, indeed, warning them by means of natural precepts, which from the beginning he had implanted in mankind, that is, by means of the decalogue (which, if any one does not observe, he has no salvation), did then demand nothing more of them." Book iv. chap. xv. sect. 1.
The precepts of the decalogue he rightly terms "natural precepts," that is, precepts which constitute "the work of the law" written by nature in the hearts of all men, but marred by the presence of the carnal mind or law of sin in the members. That this law of God pertains alike to Jews and to Gentiles, he thus affirms:--
"Inasmuch, then, as all natural precepts are common to us and to them (the Jews), they had in them, indeed, the beginning and origin; but in us they have received growth and completion." Book iv. chap. xiii. sect. 4.
It is certain that Irenæus held the decalogue to be now binding on all men; for he says of it in the quotation above, "Which if any one does not observe, he has no salvation." But, though not consistent with his statement respecting the decalogue as the law of nature, he classes the Sabbath with circumcision, when speaking of it as a sign between God and Israel, and says, "The Sabbaths taught that we should continue day by day in God's service." "Moreover the Sabbath of God, that is, the kingdom, was, as it were, indicated by created things; in which [kingdom], the man who shall have persevered in serving God shall, in a state of rest, partake of God's table." He says also of Abraham that he was "without observance of Sabbaths." Book iv. chap. xvi. sects. 1, 2. But in the same chapter he again asserts the perpetuity and authority of the decalogue in these words:--
"Preparing man for this life, the Lord himself did speak in his own person to all alike the words of the decalogue; and therefore, in like manner, do they remain permanently with us, receiving, by means of his advent in the flesh, extension and increase, but not abrogation." Section 4.
This statement establishes the authority of each of the ten commandments in the gospel dispensation. Yet Irenæus seems to have regarded the fourth commandment as only a typical precept, and not of perpetual obligation like the others.