As far as I am aware, no one supposes that Irenaeus was, ethnically or culturally speaking, a Jew. He was born, in all likelihood, in Smyrna, in Asia Minor, and that he was "a Greek." In Smyrna Irenaeus came under the influence of Polycarp, the famous bishop of Smyrna who was said to have been a disciple of (the apostle?) John and who was martyred c. 155 CE. Of particular interest when we consider Irenaeus is the idea that he was raised as a Christian rather than having been converted in adulthood. [nb: If any of my facts about Irenaeus are incorrect or currently debated, please leave corrections (with documentation) in the comments.]
I bring up this background regarding Irenaeus because there's nothing of which I'm aware that makes me think Irenaeus was unusually (or even particularly) sympathetic to "Judaism" and/or emphatically Jewish expressions of Christianity. Indeed, in Adv. Haer. 1.26.2 Irenaeus comes down especially hard on the Ebionites who "are so Judaic in their style of life, that they even adore Jerusalem as if it were the house of God." Irenaeus is particularly well-known for continuing the heresiological work begun by Justin Martyr and which would continue to find expression in the writings of Jerome, Epiphanius, John Chrysostom, and others.
In this light, I find it especially interesting that Irenaeus was emphatic in insisting on what, from one perspective at least, might be described as a "middle road." That is, Irenaeus was insistent that the peculiar Christianity practiced by the Ebionites — who rejected Paul's writings and emphasized Torah observance — was "too Jewish" (if it isn't still too early to use such language here) to be authentic Christianity (as he understood and constructed it). And yet others who identified themselves as followers of Jesus (e.g., Marcion) had, according to Irenaeus, gone too far in rejecting the God revealed in the Law and the Prophets as Jesus' Father.
In other words, even in Irenaeus' very influential writings (which, we could reasonably say, played a major role in establishing Christian identity and theology in the late second century and later), we can see that Christian identity — what it might mean to identify oneself as a follower of Jesus — was massively problematic. Like the earth orbiting the sun at a life-sustaining 90+ million miles away, Christianity in the late second century could not understand itself apart from the Israelite texts and covenants that non-Christian Jewish groups were also appropriating for themselves. But writers like Irenaeus were, I think, demonstrably anxious about circling too close to as well as about escaping the influence of "Judaism." Whatever other differences marked off "Judaism" from "Christianity," the latter worshipped YHWH, the God of the former. And though the christological pronouncements of Nicaea were still a century and half in the future (and so were unavailable to Irenaeus), Irenaeus seems to have been absolutely clear that his own adoration of Jesus did not displace YHWH as the Christian God (and the Law and the Prophets as the revelation of YHWH).
Given my current interests in the discursive work being done at this time (second century CE) to "partition" Judeo-Christianity (see Boyarin's Border Lines), I think we need to also pay attention to the ways that early Christian writers expended discursive energy to keep themselves associated with "Israel," if not with "Judaism" so-called. After all, Marcion was just as mistaken — and damned — as were the Ebionites, if I read Irenaeus correctly.
Also, I wonder what type of discursive work best suits our current situation, when "partitioning" is probably not as urgent as it seemed to be in the second century.
Irenaeus, Against Heresies 1.27:
Irenaeus, Against Heresies 1.27:
1. Cerdo was one who took his system from the followers of Simon Magus, and came to live at Rome in the time of Hyginus, who held the ninth place in the episcopal succession from the apostles downwards. He taught that the God proclaimed by the law and the prophets was not the Father of our Lord Jesus Christ. For the former was known, but the latter unknown; while the one also was righteous, but the other benevolent.
2. Marcion of Pontus succeeded him, and developed his doctrine. In so doing, he advanced the most daring blasphemy against Him who is proclaimed as God by the law and the prophets, declaring Him to be the author of evils, to take delight in war, to be infirm of purpose, and even to be contrary to Himself. But Jesus being derived from that father who is above the God that made the world, and coming into Judaea in the times of Pontius Pilate the governor, who was the procurator of Tiberius Caesar, was manifested in the form of a man to those who were in Judaea, abolishing the prophets and the law, and all the works of that God who made the world, whom also he calls Cosmocrator. Besides this, he mutilates the Gospel which is according to Luke, removing all that is written respecting the generation of the Lord, and setting aside a great deal of the teaching of the Lord, in which the Lord is recorded as most dearly confessing that the Maker of this universe is His Father. He likewise persuaded his disciples that he himself was more worthy of credit than are those apostles who have handed down the Gospel to us, furnishing them not with the Gospel, but merely a fragment of it. In like manner, too, he dismembered the Epistles of Paul, removing all that is said by the apostle respecting that God who made the world, to the effect that He is the Father of our Lord Jesus Christ, and also those passages from the prophetical writings which the apostle quotes, in order to teach us that they announced beforehand the coming of the Lord.
3. Salvation will be the attainment only of those souls which had learned his doctrine; while the body, as having been taken from the earth, is incapable of sharing in salvation. In addition to his blasphemy against God Himself, he advanced this also, truly speaking as with the mouth of the devil, and saying all things in direct opposition to the truth,-that Cain, and those like him, and the Sodomites, and the Egyptians, and others like them, and, in fine, all the nations who walked in all sorts of abomination, were saved by the Lord, on His descending into Hades, and on their running unto Him, and that they welcomed Him into their kingdom. But the serpent which was in Marcion declared that Abel, and Enoch, and Noah, and those other righteous men who sprang from the patriarch Abraham, with all the prophets, and those who were pleasing to God, did not partake in salvation. For since these men, he says, knew that their God was constantly tempting them, so now they suspected that He was tempting them, and did not run to Jesus, or believe His announcement: and for this reason he declared that their souls remained in Hades.
4. But since this man is the only one who has dared openly to mutilate the Scriptures, and unblushingly above all others to inveigh against God, I purpose specially to refute him, convicting him out of his own writings; and, with the help of God, I shall overthrow him out of those discourses of the Lord and the apostles, which are of authority with him, and of which he makes use. At present, however, I have simply been led to mention him, that thou mightest know that all those who in any way corrupt the truth, and injuriously affect the preaching of the Church, are the disciples and successors of Simon Magus of Samaria. Although they do not confess the name of their master, in order all the more to seduce others, yet they do teach his doctrines. They set forth, indeed, the name of Christ Jesus as a sort of lure, but in various ways they introduce the impieties of Simon; and thus they destroy multitudes, wickedly disseminating their own doctrines by the use of a good name, and, through means of its sweetness and beauty, extending to their hearers the bitter and malignant poison of the serpent, the great author of apostasy.