I believe that we are talking about two different things. There is Jesus the man who was the flesh body, and, the Spirit that was inside of him, which would be the Spirit of Christ.
A person can say something with his mind from his own understanding, and, it will be coming from him/herself. Now if the Spirit (or a spirit) speaks through a person, it is not the man/woman speaking, it is the Spirit or spirit speaking through them.
Jesus, who was the flesh body, would be the Son in my understanding, while, the Spirit of Christ, would be the holy Spirit, i.e., the Spirit that is holy.
It would have been the Spirit speaking through Jesus the man (the son) (Joh 6:63, Joh 14:10) when he said:
Joh 14:16 And I will pray the Father, and he shall give you another Comforter, that he may abide with you for ever;
Joh 14:17 Even the Spirit of truth; whom the world cannot receive, because it seeth him not, neither knoweth him: but ye know him; for he dwelleth with you, and shall be in you.
Joh 14:18 I will not leave you comfortless: I will come to you.
Joh 14:19 Yet a little while, and the world seeth me no more; but ye see me: because I live, ye shall live also.
Joh 14:20 At that day ye shall know that I am in my Father, and ye in me, and I in you.
Who will be in you? Christ's Spirit (obviously not Jesus in the flesh).
Also see:
Rev 19:10 And I fell at his feet to worship him. And he said unto me, See thou do it not: I am thy fellowservant, and of thy brethren that have the testimony of Jesus: worship God: for the testimony of Jesus is the spirit of prophecy.
2Pe 1:20 Knowing this first, that no prophecy of the scripture is of any private interpretation.
2Pe 1:21 For the prophecy came not in old time by the will of man: but holy men of God spake as they were moved by the Holy Ghost.
1Pe 1:10 Of which salvation the prophets have enquired and searched diligently, who prophesied of the grace that should come unto you:
1Pe 1:11 Searching what, or what manner of time the Spirit of Christ which was in them did signify, when it testified beforehand the sufferings of Christ, and the glory that should follow.
The Holy Spirit would be the spirit of prophecy (which is what the prophets prophesied by), i.e., the Spirit of Christ (1Pe 1:11).