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