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.
[...] When the spirit here blended with the soul is united to God’s handiwork, the man is rendered spiritual and perfect because of the outpouring of the Spirit, and this is he who was made in the image and likeness of God.
But if the Spirit be wanting to the soul, he who is such is indeed of an animal nature, and being left carnal, shall be an imperfect being, possessing indeed the image of God in his formation, but not receiving the similitude through the Spirit; and thus is this being imperfect.
[...] That flesh which has been moulded is not a perfect man in itself, but the body of a man, and part of a man. Neither is the soul itself, considered apart by itself, the man; but it is the soul of a man, and part of a man. Neither is the spirit a man, for it is called the spirit, and not a man; but the commingling and union of all these constitutes the perfect man.
And for this cause does the apostle, explaining himself, make it clear that the saved man is a complete man as well as a spiritual man; saying thus in the first Epistle to the Thessalonians: “Now the God of peace sanctify you perfect; and may your spirit, and soul, and body be preserved whole without complaint to the coming of the Lord Jesus Christ.”
Now what was his object in praying that these three — that is, soul, body, and spirit — might be preserved to the coming of the Lord, unless he was aware of the [future] reintegration and union of the three, and that they should be heirs of one and the same salvation? For this cause also he declares that those are “the perfect” who present unto the Lord the three component parts without offence.
Those, then, are the perfect who have had the Spirit of God remaining in them, and have preserved their souls and bodies blameless, holding fast the faith of God, that is, that faith which is directed towards God, and maintaining righteous dealings with respect to their neighbours.
Irenaeus of Lyons (2nd century AD – c. 202): Adversus Haereses, 5, 6, 1.