The truth is found in the tradition of the Apostles instituted in their Churches

It is within the power of all, therefore, in every Church, who may wish to see the truth, to contemplate clearly the tradition of the apostles manifested throughout the whole world; and we are in a position to reckon up those who were by the apostles instituted bishops in the Churches, and [to demonstrate] the succession of these men to our own times; those who neither taught nor knew of anything like what these [heretics] rave about.

…For they were desirous that these men should be very perfect and blameless in all things, whom also they were leaving behind as their successors, delivering up their own place of government to these men; which men, if they discharged their functions honestly, would be a great boon [to the Church], but if they should fall away, the direst calamity.

Irenaeus of Lyons
Against Heresies, Book III
Chapter III

The tradition of the Apostles is preserved by Apostolic Succession

But, again, when we refer them to that tradition which originates from the apostles, [and] which is preserved by means of the succession of presbyters in the Churches, they object to tradition, saying that they themselves are wiser not merely than the presbyters, but even than the apostles, because they have discovered the unadulterated truth.

…It comes to this, therefore, that these men do now consent neither to Scripture nor to tradition.

Irenaeus of Lyons
Against Heresies, Book III
Chapter II

Traditions of Gospel authorship

For, after our Lord rose from the dead, [the apostles] were invested with power from on high when the Holy Spirit came down [upon them], were filled from all [His gifts], and had perfect knowledge: they departed to the ends of the earth, preaching the glad tidings of the good things [sent] from God to us, and proclaiming the peace of heaven to men, who indeed do all equally and individually possess the Gospel of God. Matthew also issued a written Gospel among the Hebrews in their own dialect, while Peter and Paul were preaching at Rome, and laying the foundations of the Church. After their departure, Mark, the disciple and interpreter of Peter, did also hand down to us in writing what had been preached by Peter. Luke also, the companion of Paul, recorded in a book the Gospel preached by him. Afterwards, John, the disciple of the Lord, who also had leaned upon His breast, did himself publish a Gospel during his residence at Ephesus in Asia.

Irenaeus of Lyons
Against Heresies, Book III
Chapter I

The only true Church of the Apostles

Call to mind then, the things which I have stated in the two preceding books, and, taking these in connection with them, thou shalt have from me a very copious refutation of all the heretics; and faithfully and strenuously shalt thou resist them in defense of the only true and life-giving faith, which the Church has received from the apostles and imparted to her sons. For the Lord of all gave to His apostles the power of the Gospel, through whom also we have known the truth, that is, the doctrine of the Son of God; to whom also did the Lord declare: “He that hears you, hears Me; and he that despises you, despises Me, and Him that sent Me.”

Irenaeus of Lyons
Against Heresies, Book III
Chapter I

Bodiless souls exists after death before the resurrection

By these things, then, it is plainly declared that souls continue to exist that they do not pass from body to body, that they possess the form of a man, so that they may be recognized, and retain the memory of things in this world; moreover, that the gift of prophecy was possessed by Abraham, and that each class [of souls] receives a habitation such as it has deserved, even before the judgment.

Irenaeus of Lyons
Against Heresies, Book II
Chapter XXXIV

Resurrection is a resuscitation of our same bodies

And then the doctrine concerning the resurrection of bodies which we believe, will emerge true and certain [from their system]; since, [as we hold,] God, when He resuscitates our mortal bodies which preserved righteousness, will render them incorruptible and immortal.

Irenaeus of Lyons
Against Heresies, Book II
Chapter XXIX

Jesus, the first-born form the dead, existed before all

Then, at last, He came on to death itself, that He might be “the first-born from the dead, that in all things He might have the pre-eminence,” the Prince of life, existing before all, and going before all.

Irenaeus of Lyons
Against Heresies, Book II
Chapter XXII

Jesus sanctified humanity having lived the full human experience

For He came to save all through means of Himself—all, I say, who through Him are born again to God—infants, and children, and boys, and youths, and old men. He therefore passed through every age, becoming an infant for infants, thus sanctifying infants; a child for children, thus sanctifying those who are of this age, being at the same time made to them an example of piety, righteousness, and submission; a youth for youths, becoming an example to youths, and thus sanctifying them for the Lord. So likewise He was an old man for old men, that He might be a perfect Master for all, not merely as respects the setting forth of the truth, but also as regards age, sanctifying at the same time the aged also, and becoming an example to them likewise.

Irenaeus of Lyons
Against Heresies, Book II
Chapter XXII