Man is body, soul and spirit

Now the soul and the spirit are certainly a part of the man, but certainly not the man; for the perfect man consists in the commingling and the union of the soul receiving the spirit of the Father, and the admixture of that fleshly nature which was moulded after the image of God.

Irenaeus of Lyons
Against Heresies, Book V
Chapter II

The cup is the communion of his blood

But vain in every respect are they who despise the entire dispensation of God, and disallow the salvation of the flesh, and treat with contempt its regeneration, maintaining that it is not capable of incorruption. But if this indeed does not attain salvation, then neither did the Lord redeem us with His blood, nor is the cup of the Eucharist the communion of His blood, nor the bread which we break the communion of His body.

Irenaeus of Lyons
Against Heresies, Book V
Chapter II

His soul for our souls, His flesh for our flesh

Since the Lord thus has redeemed us through His own blood, giving His soul for our souls, and His flesh for our flesh, and has also poured out the Spirit of the Father for the union and communion of God and man, imparting indeed God to men by means of the Spirit, and, on the other hand, attaching man to God by His own incarnation, and bestowing upon us at His coming immortality durably and truly, by means of communion with God,—all the doctrines of the heretics fall to ruin.

Irenaeus of Lyons
Against Heresies, Book V
Chapter I

Man can choose good or evil

Since God, therefore, gave [to man] such mental power man knew both the good of obedience and the evil of disobedience, that the eye of the mind, receiving experience of both, may with judgment make choice of the better things; and that he may never become indolent or neglectful of God’s command;

Those persons, therefore, who have apostatized from the light given by the Father, and transgressed the law of liberty, have done so through their own fault, since they have been created free agents, and possessed of power over themselves.

Irenaeus of Lyons
Against Heresies, Book IV
Chapter XXXVIII

God gave us free will

This expression [of our Lord], “How often would I have gathered thy children together, and thou wouldest not,” set forth the ancient law of human liberty, because God made man a free [agent] from the beginning, possessing his own power, even as he does his own soul, to obey the behests of God voluntarily, and not by compulsion of God.

2…But since all men are of the same nature, able both to hold fast and to do what is good; and, on the other hand, having also the power to cast it from them and not to do it…

4…But because man is possessed of free will from the beginning, and God is possessed of free will, in whose likeness man was created, advice is always given to him to keep fast the good, which thing is done by means of obedience to God.

5. And not merely in works, but also in faith, has God preserved the will of man free and under his own control saying, “According to thy faith be it unto thee;” thus showing that there is a faith specially belonging to man, since he has an opinion specially his own.

Irenaeus of Lyons
Against Heresies, Book IV
Chapter XXXVII

Biblical interpretation must be done in light of catholic tradition

But here some one perhaps will ask, Since the canon of Scripture is complete, and sufficient of itself for everything, and more than sufficient, what need is there to join with it the authority of the Church’s interpretation? For this reason—because, owing to the depth of Holy Scripture, all do not accept it in one and the same sense, but one understands its words in one way, another in another; so that it seems to be capable of as many interpretations as there are interpreters. For Novatian expounds it one way, Sabellius another, Donatus another, Arius, Eunomius, Macedonius, another, Photinus, Apollinaris, Priscillian, another,Iovinian, Pelagius, Celestius, another, lastly, Nestorius another. Therefore, it is very necessary, on account of so great intricacies of such various error, that the rule for the right understanding of the prophets and apostles should be framed in accordance with the standard of Ecclesiastical and Catholic interpretation.

Moreover, in the Catholic Church itself, all possible care must be taken, that we hold that faith which has been believed everywhere, always, by all. For that is truly and in the strictest sense Catholic, which, as the name itself and the reason of the thing declare, comprehends all universally. This rule we shall observe if we follow universality, antiquity, consent. We shall follow universality if we confess that one faith to be true, which the whole Church throughout the world confesses; antiquity, if we in no wise depart from those interpretations which it is manifest were notoriously held by our holy ancestors and fathers; consent, in like manner, if in antiquity itself we adhere to the consentient definitions and determinations of all, or at the least of almost all priests and doctors.

St. Vincent of Lerins
Commonitory
Chapter 2:5-6

The OT prophets were also the body of Christ

For the prophets prefigured in themselves all these things, because of their love to God, and on account of His word. For since they themselves were members of Christ, each one of them in his place as a member did, in accordance with this, set forth the prophecy [assigned him]; all of them, although many, prefiguring only one, and proclaiming the things which pertain to one.

Irenaeus of Lyons
Against Heresies, Book IV
Chapter XXXIII