Consider first that among the things we know about God via natural theology, at least from an Aristotelian-Thomistic (A-T) point of view (where the relevant A-T arguments are defended at length in The Last Superstition and Aquinas), are that His attributes include intellect and will. But since possession of intellect and will is definitive of persons, it follows that God cannot correctly be referred to as an “it” or in any other impersonal terms. (It is true that for A-T, terms like “intellect” and “will” apply to God in an analogical rather than a univocal sense, but that does not affect the point. For what it means to say that there is in God something analogous to intellect and will in us does not make God less than personal; quite the opposite.)
So, only personal terms will do. But why “He” rather than “She”? Well, consider further that from the point of view of classical natural law theory, the fundamental natural social institution – the family – has the father as its head. Obviously this is a large and controversial topic, and one I have no intention of getting into here in any detail. Suffice it to say that the claim is not that men are morally superior to women, or that they have dictatorial rights over their wives and children, or that all men are born leaders and all women born followers. The claim is rather that in any orderly social arrangement there must be some ultimate authority, and that nature has ordained that at least in the normal case it is in the father in whom this authority resides. For when human beings are living in accordance with what the natural law requires of them in the area of sexual morality, families will tend to be large. Obviously this would put a very great burden on mothers if there were no one to protect and provide for them and their children, but protecting and providing for them is precisely what a father is supposed to do. And that, from the point of view of natural law theory, is why men tend to be more assertive and oriented to the public rather than the domestic realm, and thus more oriented toward leadership. Obviously there are exceptions, but for natural law theory it is the normal case that determines the content of morality.
Again, this is a large topic, and since the subject of the post is theology rather than ethics or feminism, I’m not going to pursue it further. The point for our purposes is that at least from the perspective of the moral theory associated with A-T, paternal and thus masculine imagery is naturally going to be regarded as the appropriate sort to use when characterizing God’s relationship to His creatures. For they are dependent on Him in a way comparable to a family’s dependence on a father; and He has authority over them comparable to the authority a father has over his family.
That is one consideration. A second has to do with the way God creates. From a classical theistic perspective, God creates the world ex nihilo rather that out of His own substance. Creation is thus in no way comparable to gestation and birth, imagery which, when applied to theology, suggests either pantheism or a pagan cosmogony. The divine creative act is more like the relatively “distant” role played by the father in procreation. Accordingly, paternal and thus masculine imagery better conveys God’s transcendence.
Again, these considerations derive entirely from what can be known about God through purely philosophical arguments. But there are also considerations deriving from divine revelation. Not the least of these is that when God took on human flesh, He did so precisely as a man rather than as a woman – which is exactly what we should expect given the considerations drawn from natural theology. Furthermore, the Incarnation involved God’s miraculously causing a woman to become pregnant, of its nature a masculine act. And the Holy Trinity of which Jesus Christ is the second Person is of course a Trinity of Father, Son, and Holy Spirit – masculine descriptions of this sort being, again, exactly what we would expect given what we know of God via the purely philosophical arguments.
Moreover, the entire Christian understanding of salvation presupposes a masculine conception of God. Individual human souls (whether those of men or women) have, given their dependence on God, always been conceived of in the Christian tradition in female terms, e.g. as virgins awaiting their Bridegroom (Matthew 25: 1-13). The faithful are also characterized as children of Holy Mother Church, who is the Bride of Christ. The point of this imagery is that the role of the Church relative to the faithful is comparable to that of a mother who nourishes her child in the womb in preparation for birth – the “birth” in the case of the faithful being their entry into eternal life. And God protects and provides for the Church and the faithful as a husband and father does his wife and children.
To suggest that God might be described as a mother or wife would make nonsense of all of this, and (given the outré sexual imagery it would suggest) add blasphemy into the bargain. And it can have no justification whatsoever in either reason or revelation. Feminists who pretend otherwise are worshipping a god of their own invention. There’s a name for that sort of thing.
(All of these considerations are, by the way, relevant to the question of why from a Catholic point of view women can never in principle be ordained priests. For the priest is an alter Christus, “another Christ,” who absolves us of our sins and transforms mere bread and wine into divine flesh and blood. He is the father of his flock. His role is God-like, and thus, given what has been said, essentially masculine. Even the greatest human being ever to have lived other than Christ Himself – His Blessed Mother – was not made by Him a “priestess.” Yet the honor in which she is held by the Church and the faithful – honor which the Church’s enemies typically claim is excessive – gives the lie to the calumny that the Church is “misogynist.” But I digress.)