Coming to the third person of the Trinity in Bossuet’s Elevations on the Mysteries, 2,5:
God is thus fertile, God has a Son: but where is the Holy Spirit here, and where is the holy and perfect Trinity which we serve from our baptism onwards? Does not God love this Son and is he not loved? This love is neither imperfect nor accidental in God: the love of God is substantial, like his thought; and, the Holy Spirit who comes from the Father, from the Father and the Son, as their mutual love, is the same substance one to the other: a third consubstantial, and with them the same God.
But why is he not Son, although he is by production the same nature? God has not revealed it. He has well said that the Son be unique, because he is perfect and all which is perfect is unique, and if he can have two sons, the generation of the son would be imperfect. All which came afterwards, will not be son, and will not come by generation, although of the same nature. What will thus be this last production of God? It is a procession, without a particular name: the Holy Spirit proceeds from the Father: the Holy Spirit is the common spirit of the Father and the Son: the Holy Spirit takes from the Son and the Son sends him like the Father. Human reasonings, shut up: God wanted to explain that the procession of his Word was a true and perfect generation: that which was the procession of his Holy Spirit, he did not want to say, except that there was nothing in nature which represented an action so substantial and entire and singular. It is a secret reserved for the happy vision.
O God Holy Spirit, you are not Son, since you are the eternal love and subsistant of the Father and the Son: who supposes by consequence the generated Son, and generated like the unique Son because he is perfect. You are perfect also and unique in your genre, and in your order: you are not a foreigner to the Father and to the Son, since you are their mutual love: those you want to separate them, separate themselves one from another and divide their eternal reign.
You are equal to the Father and to the Son, since we are equally consecrated in the name of the Father and the Son and the Holy Spirit, and you have with them, the same temple which is our soul, our body, all that we are. Nothing unequal nor foreign to the Father and the Son ought to be named with them in equality: I do not want to be baptised and consecrated in the name of a trustee. I do not want to be the temple of a creäture: this would be idolatry to build him a temple and, moreover, to be and believe oneself as his temple.