13 Consider, beloved, why also was there a something pointed out by means of the dove, as that the dove— namely, the Holy Spirit in the shape of a dove— came to the Lord on being baptized, and rested upon Him, while by the coming of the dove John learned this, that there dwelt in the Lord a power peculiarly His own to baptize? Because it was by this power peculiar to Himself, as I have said, the peace of the Church was made secure. And yet it may be that one may have baptism apart from the dove; but that baptism apart from the dove should do him good, is impossible.
Consider, beloved, and understand what I say, for by this deception they mislead such of our brethren as are dull and cold. Let us be more simple and more fervent. See, say they, have I received, or have I not? I answer, You have received. Well, if I have received, there is nothing which you can give me; I am safe, even on your own evidence. For I affirm that I have received, and you, too, confess that I have received: I am safe by the confession of both: what then do you promise me? Why would you make me a Catholic, when you would not give me anything further, seeing you confess that I have already received that which you affirm yourself to possess? But when I say, Come to me, I say that you do not possess, who yet confessest that I do. Why do you say, Come to me?
Source: Tractates on the Gospel of John (New Advent)