If Jesus was resurrected as a man how can Paul say his apostleship was not through a man but it was through Jesus at Galatians 1:1?

Yes, Jesus was resurrected like a new human being. What Paul is trying to say is that his teaching is not of human origin like religious tachings are. He is trying to say he didn't got his doctrine from human sources, but from Jesus, who is the Son of God.

The Greek text does not say "a man". It is not talking in the singular about any one man. It states, "...not from men..." Rather, this is a collective form, speaking of humanity. Paul was not authorised for his task through men, that is, through any one body of mankind (e.g. the Sanhedrin or any other body). His authority came from Heaven, through a personal commission by the risen Lord Jesus Christ, in conjunction and perfect harmony with God the Father. The authorising body was the Godhead, from Heaven.

A few verses further on Paul pointed out to the Galatian Christians that it was the Holy Spirit who ministered to them, to grant them the hearing of faith which saves, as opposed to the works of the law (Galatians 3:2). That same Holy Spirit empowered, and thus authorised, the ministry of Paul. I repeat, the authorising body was the Godhead, from Heaven.

The question, which I am answering (as it stands at 19:09 GMT on 03 February 2020) is :

How can Paul say his apostleship is not from men, neither through man ?

Paul makes clear in Galatians 1:1 that his apostleship was not through man, or by man. It was through Jesus Christ and through God Father (literal). If not through man or by man and if through (that is to say by the agency of an intermediary) Jesus Christ and God Father, then who was the originator of this apostleship ?

I would say it is the same person as Paul refers to in connection with eldership :

Take heed therefore unto yourselves, and to all the flock, over the which the Holy Ghost hath made you overseers, to feed the church of God, which he hath purchased with his own blood. [Acts 20:28 KJV]

The Holy Spirit made certain men overseers at Ephesus. The 'blood of his own' (literal) is that with which God (the Holy Spirit) purchased the gathered company at Ephesus. And it was God, the Holy Spirit, who appointed individuals to oversee that gathered company.

Likewise, Paul's apostleship as to the intermediary agency (through) is Jesus Christ and God Father. But if through those two persons, then who was the instigator ?

None other than the same Holy Spirit who made overseers at Ephesus.

And we see that all the company of the redeemed are so appointed :

Forasmuch as ye are manifestly declared to be the epistle of Christ ministered by us, written not with ink, but with the Spirit of the living God; not in tables of stone, but in fleshy tables of the heart. [2 Corinthians 3:3 KJV]

By the personal operations of the Holy Spirit, under the intermediary agency of the ministry of the apostle, the Spirit of the Living God wrote upon the hearts of those who received that word and they became living epistles, known and read of all men.

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Thus none of this is of man or by man.

It is not human in origin. It is of Spirit. Holy Spirit.

Whether the birth of God's children . . . .

Which were born, not of blood, nor of the will of the flesh, nor of the will of man, but of God. [John 1:13 KJV.

Or the making of overseers . . .

Or the calling and sending of an apostle . . . .

. . . all is of God, who is Spirit (John 4:24).

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It was the Holy Spirit who, after the conversion of Saul of Tarsus and after some time during which he had fellowship with other Christians, marked out Barnabas and Saul :

As they ministered to the Lord, and fasted, the Holy Ghost said, Separate me Barnabas and Saul for the work whereunto I have called them. [acts 13:2 KJV]

This is not of man, but of God.

Nor was the conversion of Saul anything to do with men, for it was a voice from heaven and a light above the brightness of the sun which came upon him on the road to Damascus.

Jesus Christ spoke to Saul, but Jesus Christ did not appear, bodily.

Risen from the dead, Jesus said :

Behold my hands and my feet, that it is I myself: handle me, and see; for a spirit hath not flesh and bones, as ye see me have. [Luke 24:39 KJV]

And they gave him a piece of a broiled fish, and of an honeycomb. And he took it, and did eat before them. [Luke 24: 42, 43 KJV]

Jesus rose bodily, they handled him, he ate food in front of them.

And he ascended into heaven.

And from there, from the throne of God, as God, he appointed Paul to be an apostle by the direction of God, the Holy Spirit.

I don't believe that the nature of Christ's resurrected body needs to be a part of the answer. Paul is creating a distinction here in Galatians 1:1

Paul, an apostle - not from men nor through man, BUT through Jesus Christ and God the Father...

in order to establish the source of his authority. A great deal of this entire epistle is a defense of his apostleship and he goes to such great lengths as to specifically point out that when he first received revelation of Jesus Christ he did not go running to Jerusalem for approval from those who appeared to be influential but did go later to make sure that they were not at odds with one another in their similar but separate ministries to Jew and Gentile.

It is quite clear throughout this epistle (which mirrors that of Scripture) that he draws this same distinction between authority which is of human origin and authority of divine origin:

For am I now seeking the approval of man, or of God? Or am I trying to please man? If I were still trying to please man, I would not be a servant of Christ. - Galatians 1:10

Some person or persons had come into the Galatian churches and called Paul's apostleship into question in order to change the gospel which he preached to them and which they had received from him and bring them back under the Law. Paul defends the source of his apostolic authority in order to defend his apostolic message which is referred to by him as the Gospel of God.

He is saying that his apostolic authority does not come "from men"(not the Jerusalem council, Sanhedrin, or any other earthly ruling body) "nor through (a) man" (not himself, Peter or James, or any earthly individual) but through Jesus Christ and God the Father. This is not a comparison between "a man" and the man, Christ Jesus. It is, rather, a distinction between human and Divine authority.

St. Paul is saying that Jesus is not "man" in the sense he here refers to: "a mere man." Rather, Jesus, "who, being in the form of God, deemed not equality with God robbery, but humbled himself, taking the form of a servant: being made in the likeness of men, and in habit also found as man." (Phil. 2:6-7)

From (apo) means "apostle sent from" and by (dia) means "made an apostle by the authority of."

John 20:27-28 (DRB) Then he saith to Thomas: Put in thy finger hither, and see my hands; and bring hither thy hand, and put it into my side; and be not faithless, but believing. Thomas answered, and said to him: My Lord, and my God.