God Is Masculine
The source for the reason why God is masculine is Peter Kreeft’s speech “Women and the Priesthood.” He says that God is masculine, because He “impregnates” the soul from the outside with grace. I add that there are reasons why each person of the Trinity could be called masculine.
The first person, because (1f) He as Creator and in His capacity as a perfect agent or pure act created matter and imbued it with form, and that which acts is masculine, while that which is acted upon is feminine; and (2f) as Father He rewards and punishes those He loves, an activity which properly belongs to the father not the mother (or at least, to the masculine part of every human being).
The second person, because (1s) as Redeemer it belongs to the man to sacrifice himself for his bride rather than to the woman for her bridegroom; and (2s) Jesus was male (of course, this only shows the sex of His human nature not His divine nature, but it would be odd indeed if the divine Daughter was incarnated as a male).
The third person, because (1h) as Sanctifier, as Kreeft states, He gives grace which bears fruit, etc.