Do you see that all through Scripture the Spirit is preached, and yet nowhere named a creature? And what can the impious have to say if the Lord sends forth His disciples to baptize in the name of the Father, and of the Son, and of the Holy Spirit? Without contradiction, that implies a communion and unity between them, according to which there are neither three divinities nor (three) lordships; but, while there remain truly and certainly the three persons, the real unity of the three must be acknowledged. And in this way proper credit will be given to the sending and the being sent (in the Godhead), according to which the Father has sent forth the Son, and the Son in like manner sends forth the Spirit. For one of the persons surely could not (be said to) send Himself; and one could not speak of the Father as incarnate. For the articles of our faith will not concur with the vicious tenets of the heresies; and it is right that our conceptions should follow the inspired and apostolic doctrines, and not that our impotent fancies should coerce the articles of our divine faith.
Source: A Sectional Confession of Faith (New Advent)