There is one God, who by his Word and Wisdom made and ordered all things. His Word is our Lord Jesus Christ who in these last times became a man among men, that he might unite the end with the beginning, that is, Man with God. Therefore the prophets who received from this same Word their prophetic gift, proclaimed his advent in the flesh, by which was effected the mingling and uniting of God and man according to the Father’s pleasure. For the Word of God foretold from the beginning that God would be seen by men and would live with them on earth and converse with them; that he would be present with his creatures to bring salvation to them and to be perceived by them that he would free us from the hands of those who hate us, that is, from the whole spirit of transgression; and would make us serve him all our days in holiness and righteousness; that man, taking to himself the Spirit of God, would pass to the glory of the Father.
The prophets therefore indicated beforehand that God would be seen by men; as the Lord also says, ‘Blessed are the pure in heart, for they shall see God.’
I grant that in respect of his greatness and marvellous glory, no man shall see God and live, for the Father is incomprehensible. But in respect of his love and kindly mercy, and of his infinite power, he grants even this to such as love him, I mean, to see God, as the prophets also foretold. Because the things which are impossible with men are possible with God.
Man does not see God by his own powers; but God of his own will appears to men, to whom he wills, and when he wills, and as he wills. For God can do all things: he was seen in former times prophetically through the Spirit, he is seen in the Son by adoption, and he will be seen in the kingdom of heaven as Father. The Spirit prepares man for the Son of God, the Son brings him to the Father, and the Father bestows on him incorruptibility for eternal life, which comes to everyone from his beholding God.
As those who see the light are in the light, and partake of its splendour, so those who see God are in God, partaking of his splendour. But God’s splendour gives life; those therefore who see God will partake of life.
Treatise of St Irenaeus Against the Heresies Bk 4,20, 4–5.
from The Office of Readings for the Wednesday of the Third week in Advent,
The Divine Office.